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Thread: Hydraulics myths

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    Hydraulics myths

    I recently needed to re-subscribe to a hydraulics newsletter, and as a consequence I'm receiving back issues.

    The one below took me a while to understand when I first read it a few years ago, so I thought I'd post here (it's short) for others to contemplate. I doubt the author would complain.

    "Hello John,

    In your last hydraulics bulletin, I exploded the myth about pump suction strainers - they do more harm than good. And installing them to 'protect' the pump is a contradiction because they can actually destroy it.
    Here's another big myth ...
    Myth #2. Drift in a double-acting cylinder is always caused by a leaking piston seal.
    A popular misconception about hydraulic cylinders is that if the piston seal is leaking, the cylinder will automatically drift down.
    The reality is, if the piston seal is completely removed from a double-acting cylinder, the cylinder is completely filled with oil and the ports are plugged, the cylinder will hold its load indefinitely - unless the rod-seal leaks.
    What happens under these conditions - due to the unequal volume either side of the piston, is fluid pressure equalizes and the cylinder becomes hydraulically locked. Once this occurs, the only way the cylinder can move is if fluid escapes from the cylinder via the rod seal or its ports.
    If you grasp the theory at work here, you'll probably realize there are a couple of exceptions. The first is a double-rod cylinder - where volume is equal on both sides of the piston.
    And the second is when a load is hanging on a double-acting cylinder. In this arrangement, the volume of pressurized fluid on the rod side can be accommodated on the piston side. In this case a vacuum will develop on the piston side and depending on the weight of the load, this may eventually result in equilibrium that arrests further drift.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Author of Insider Secrets to Hydraulics
    Last edited by john maddock; 10-04-21 at 09:43 PM. Reason: Clarity
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    Re: Hydraulics myths

    The bit to consider in an effort to understand the principle are the ideals required, ie the gland seal being 100% leak proof and the ports being fully sealed! Not something that often occurs in some systems under working conditions?

    I've found that one trick to use on hydraulics is to imagine what the oil is being made to do internally in components although some systems can be fiendishly complicated and hard to follow.
    A Pea Viner course I went on in the 80's was made extremely complicated by the instructors employed by the manufacturer, at first we all though it was because these fellows from the Nottingham Mining industry were teaching us all about some new radical techniques and we just couldn't grasp what they were trying to get us to understand, then by the 3rd day the pennies could be heard dropping as one after another, we all began to understand where they were coming from and it all fell into place!!

    Of course, now 35+yrs on the complexities of some hydraulic systems have become mind boggling, same go for todays electrical & electronic systems too.
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    Re: Hydraulics myths

    Quote Originally Posted by Footsfitter View Post
    The bit to consider in an effort to understand the principle are the ideals required, ie the gland seal being 100% leak proof and the ports being fully sealed! Not something that often occurs in some systems under working conditions?

    I've found that one trick to use on hydraulics is to imagine what the oil is being made to do internally in components although some systems can be fiendishly complicated and hard to follow.
    A Pea Viner course I went on in the 80's was made extremely complicated by the instructors employed by the manufacturer, at first we all though it was because these fellows from the Nottingham Mining industry were teaching us all about some new radical techniques and we just couldn't grasp what they were trying to get us to understand, then by the 3rd day the pennies could be heard dropping as one after another, we all began to understand where they were coming from and it all fell into place!!

    Of course, now 35+yrs on the complexities of some hydraulic systems have become mind boggling, same go for todays electrical & electronic systems too.
    FF wrote:

    Of course, now 35+yrs on the complexities of some hydraulic systems have become mind boggling, same go for todays electrical & electronic systems too.[/QUOTE]

    Not wrong, FF, although -ignoring the control valves - at least you can trace the flow of oil through pipes. It's just a tad more difficult to trace the flow of electrons in an integrated circuit.

    Here's the next hydraulics myth from Brendan Casey:

    Myth #3. New hydraulic oil is clean hydraulic oil.
    New hydraulic oil straight from the drum, has a typical cleanliness level of ISO 4406 23/21/18.
    Now that number may not mean a lot to you, but it's four cleanliness code levels below that considered ideal for a high pressure, high performance hydraulic system.
    Looking at it another way, a 25 GPM pump operating continuously in hydraulic oil at 23/21/18 will circulate 3,500 pounds of dirt to the hydraulic system's components each year.
    To add hydraulic oil, and not the dirt, always filter new oil prior to use in a hydraulic system.
    This can be accomplished by pumping the oil into the hydraulic reservoir through the system's return filter. The easiest way to do this is to install a tee in the return line and attach a quick-connector to the branch of this tee.
    Attach the other half of the quick-connector to the discharge hose of a drum pump.
    When hydraulic oil needs to be added to the reservoir, the drum pump is coupled to the return line and the oil is pumped into the reservoir through the return filter.
    As well as filtering the oil, spills are avoided and the ingress of external contamination is prevented.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Author of Insider Secrets to Hydraulics
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    At the viner course we had slides showing under a microscope the differences of "new oil" and oil filtered to a higher standard which was very noticeable. Way before the New Viner course the Pea Group modified the old machines by blanking off the filler, mounting a small mini-digger style engine filter right up on the top of the machine, and then using a "revolver" filtering unit to pump the oil into the tank (used a genny out in the field to power it) The revolver was used out of season to clean and condition the oil because it had two large finer filters than the machines own return filters thus improving the oil out of the barrel and later when in service.

    That modification made a huge impact the first year it was implemented. poor hygiene in difficult field circumstances had been a big issue in breakdowns, it didn't eliminate them but it made a huge difference in one simple mod.
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    Re: Hydraulics myths

    Quote Originally Posted by Footsfitter View Post
    At the viner course we had slides showing under a microscope the differences of "new oil" and oil filtered to a higher standard which was very noticeable. Way before the New Viner course the Pea Group modified the old machines by blanking off the filler, mounting a small mini-digger style engine filter right up on the top of the machine, and then using a "revolver" filtering unit to pump the oil into the tank (used a genny out in the field to power it) The revolver was used out of season to clean and condition the oil because it had two large finer filters than the machines own return filters thus improving the oil out of the barrel and later when in service.

    That modification made a huge impact the first year it was implemented. poor hygiene in difficult field circumstances had been a big issue in breakdowns, it didn't eliminate them but it made a huge difference in one simple mod.
    A very interesting comment, FF. I'm not familiar with a "revolver". What is it & how does it work?

    JV
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    Re: Hydraulics myths

    Revolver may of been a trade name for the ones back then in the 80/90's. This is the sort of thing-

    https://hyquip.co.uk/hydac-filtratio...70-m-z-bm.html


    Basically an electric motor & pump, a filter unit, and suction/delivery hoses. Some like we had used spin-on cartridge filters or like this hydac one may have a pot and element type filter. When the Pea viner groups mechanic was doing their winter maintenance any machine brought into the workshop, or even if they were parked in the machinery shed they could be connected up and the filter unit left on to circulate and clean the oil with finer micron filters, plus there was the benefit of pumping oil through one of the filter machines to add/top-up oil- in the field a 200ltr barrel was mounted on the fuel bowser in a cradle, fitted with a male QRC we would use the generator in the maintenance landrover to power the conditioning pump having just wiped and coupled up the hose connectors so no contamination from dirt,dust, mud etc like before and the new oil was also filtered to a better standard than it left the blenders! Hence why problems and breakdowns improved.
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    Re: Hydraulics myths

    Quote Originally Posted by Footsfitter View Post
    Revolver may of been a trade name for the ones back then in the 80/90's. This is the sort of thing-

    https://hyquip.co.uk/hydac-filtratio...70-m-z-bm.html


    Basically an electric motor & pump, a filter unit, and suction/delivery hoses. Some like we had used spin-on cartridge filters or like this hydac one may have a pot and element type filter. When the Pea viner groups mechanic was doing their winter maintenance any machine brought into the workshop, or even if they were parked in the machinery shed they could be connected up and the filter unit left on to circulate and clean the oil with finer micron filters, plus there was the benefit of pumping oil through one of the filter machines to add/top-up oil- in the field a 200ltr barrel was mounted on the fuel bowser in a cradle, fitted with a male QRC we would use the generator in the maintenance landrover to power the conditioning pump having just wiped and coupled up the hose connectors so no contamination from dirt,dust, mud etc like before and the new oil was also filtered to a better standard than it left the blenders! Hence why problems and breakdowns improved.
    Good info, FF. Thankyou.

    Which filters have the best filtering capacity: engine oil or fuel?

    JV
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    Re: Hydraulics myths

    Quote Originally Posted by john maddock View Post
    Good info, FF. Thankyou.

    Which filters have the best filtering capacity: engine oil or fuel?

    JV
    My answer has to be- a good quality one in either application.

    Some people have terrible hygiene standards when it come to decanting oil into engines- dirty jugs and funnels, dirt and dust in with the oil type of thing

    Likewise there are those who push their luck with fuel storage and again like above in how they get it into the fuel tank!

    I suppose the award for best filtering capacity has to go to the paper element filter on old Massey Fergusons like your old beast?

    On the farm where I grew up, the not so bright with modern machinery of the two brothers who owned the farm was renowned for draining the engine oil and filling with new but the with the filter element, being a spend thrift he used to take the element out and wash it in diesel before putting it back in again time after time!
    Eventually there was a change in brand to a Ford 6600 and then he was forever complaining thereafter about the expensive waste of money on the new tractor because he could no longer wash the filter element out seeing as it was sealed in the metal spin on filter casing!
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    Re: Hydraulics myths

    [QUOTE=Footsfitter;312519]My answer has to be- a good quality one in either application.

    Some people have terrible hygiene standards when it come to decanting oil into engines- dirty jugs and funnels, dirt and dust in with the oil type of thing

    Likewise there are those who push their luck with fuel storage and again like above in how they get it into the fuel tank!

    Ha! Reminds me of my fuel tank story!

    Many moons ago, SWMBO had a Mazda 929 car. On irregular occasions, as she was driving to work, the engine would die slowly. First time it happened, the RACT man found and changed the small fuel filter. Second time, she called me. I followed the RACT man's action and (not having a new filter), shook the petrol out of the old one (noting a lot of rust particles) & re-installed it. The car ran fine for quite a while. After a few more events, it dawned on me that the problem appeared only after the car was refueled from the farm's bulk petrol tank within a day of delivery. The delivery stirred up the rust, and the car's recirculating fuel system (it was a carburetored engine, the model before fuel injection was introduced) took about 10 minutes to filter out the rust particles, blocking the small filter and starving the engine of fuel.

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    Re: Hydraulics myths

    In your last hydraulics bulletin, I explained how to add oil to a hydraulic system - without the dirt.
    Today I want to clear up another popular misconception, about the installation of hydraulic components ...
    Myth #4. Because oil circulates through hydraulic components in operation, no special attention is required during installation beyond bolting the component on and connecting its hoses.
    Nothing could be further from the truth, as this example illustrates: I recently conducted failure analysis on a hydraulic motor that was the subject of a warranty claim. The motor had failed after only 500 hours in service, some 7,000 hours short of its expected service life.
    Inspection revealed that the motor's bearings had failed through inadequate lubrication, as a result of the hydraulic motor being started with insufficient oil in its case (housing).
    After this motor was installed, its case should have been filled with clean hydraulic oil prior to start-up. Starting a piston-type motor or pump without doing so, is similar to starting an internal combustion engine with no oil in the sump - premature failure is pretty much guaranteed.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Author of Insider Secrets to Hydraulics
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    Another mythbuster from Brendan Casey - much more esoteric, this time.

    JV

    Today I want to clarifiy another myth, that causes a lot of hydraulic problems - and even failures ...
    Myth #5. All oil returning to the hydraulic reservoir should be filtered.
    True. With one VERY important exception: The case drains of hydraulic piston pumps and motors. Connecting case drain lines to return filters can cause excessive case pressure, which has a number of damaging effects.
    High case pressure results in excessive load on the lip of the shaft seal. This causes the seal lip to wear a groove in the shaft, which eventually results in a leaking shaft seal.
    The effect of high case pressure on in-line piston pumps is the same as excessive vacuum at the pump inlet. Both conditions put the piston ball and slipper-pad socket in tension during intake.
    In severe cases this can result in buckling of the piston retaining plate and/or separation of the bronze slipper from the piston, causing major failure.
    Under certain conditions, high case pressure can cause the pistons of radial piston motors to be lifted off the cam during outlet. When this happens, the pistons are hammered back onto the cam during inlet, destroying the motor.
    For the reasons described above, conventional depth filters are generally NOT recommended on case drain lines.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Author of Insider Secrets to Hydraulics
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    Hello John,
    In your last several hydraulics bulletins I've exploded five popular hydraulics myths. And I invited you to get YOUR copy of Insider Secrets to Hydraulics.
    Today I want to switch gears and talk about a major cause of rod-seal failure in hydraulic cylinders.
    As a product group, hydraulic cylinders are almost as common as pumps and motors combined. They are less complicated than other types of hydraulic components and are therefore relatively easy to repair.
    As a result, many hydraulic equipment owners or their maintenance personnel repair hydraulic cylinders themselves. And this is why I included a whole chapter about carrying out effective repairs on hydraulic cylinders in 'Insider Secrets to Hydraulics'.
    An important step in the repair process that is often overlooked by do-it-yourself repairers, is checking rod straightness.
    Bent rods place load on the rod seal causing distortion, and ultimately premature failure of the seal. So rod straightness should always be checked when hydraulic cylinders are being re-sealed or repaired.
    The procedure for doing this is explained in detail on pages 82 and 83 of Insider Secrets to Hydraulics
    In most cases, bent rods can be straightened in a press. It is sometimes possible to straighten them without damaging the hard-chrome plating, however if the chrome is damaged, the rod must be either re-chromed or replaced.
    BUT a word of CAUTION before I go. Attempting to straighten induction-hardened rods can cause the hardened case to shatter - with the potential for serious personal injury and/or property damage.
    For this reason, before attempting to straighten any cylinder rod - make sure it hasn't been induction-hardened first.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Author of Insider Secrets to Hydraulics
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    More from Brendan Casey:

    Hello John,
    In your last couple of hydraulics bulletins, we talked about how to avoid troubleshooting mistakes by checking and eliminating the easy things first. AND I invited you to download my hydraulic troubleshooting app for your smart phone or tablet.
    Today I want to move onto how to determine the condition of the hardest working component of a hydraulic system - the pump.
    As a pump wears in service, internal leakage increases and therefore the percentage of flow available to do useful work (volumetric efficiency) decreases.
    If volumetric efficiency falls below a level considered acceptable for the application, the pump will need to be overhauled.
    In a condition-based maintenance environment, the decision to change-out the pump is often based on remaining bearing life or deterioration in volumetric efficiency, whichever occurs first.
    Volumetric efficiency is the percentage of theoretical pump flow available to do useful work. It is calculated by dividing the pump's actual output in liters or gallons per minute by its theoretical output, expressed as a percentage. Actual output is determined using a flow-tester to load the pump and measure its flow rate.
    Because internal leakage increases as operating pressure increases and fluid viscosity decreases, these variables should be stated when stating volumetric efficiency.
    For example, a hydraulic pump with a theoretical output of 100 GPM, and an actual output of 94 GPM at 5000 PSI and 120 SUS is said to have a volumetric efficiency of 94% at 5000 PSI and 120 SUS.
    When calculating the volumetric efficiency of a variable displacement pump, internal leakage must be expressed as a constant.
    To understand why this is so, think of the various leakage paths within a hydraulic pump as fixed orifices. The rate of flow through an orifice is dependent on the diameter (and shape) of the orifice, the pressure drop across it and fluid viscosity.
    This means that if these variables remain constant, the rate of internal leakage remains constant, independent of the pump's displacement.
    A real world example, which shows how costly it can be if you don't understand this concept, is detailed on pages 29 - 30 of The Hydraulic Troubleshooting Handbook

    Yours for better hydraulics knowledge,
    Brendan Casey



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    Re: Hydraulics myths

    The next installment from Brendan Casey:info too good to not pass it on


    Hello John,
    In your last hydraulics bulletin, I explained how to use volumetric efficiency to correctly determine the condition of a hydraulic pump.
    Today I want to continue on this tack and talk about testing hydraulic cylinders.
    The conventional way of testing the integrity of the piston seal in a double-acting cylinder is to pressurize the cylinder at the end of stroke and measure any leakage past the seal. This is commonly referred to as "end-of-stroke bypass test"
    The major limitation of the end-of-stroke bypass test, is it generally doesn't reveal ballooning of the cylinder tube caused by hoop stress as a result of under designed cylinder wall thickness or reduction of wall thickness through excessive honing.
    The ideal way to test for ballooning of the cylinder tube is to conduct a piston-seal bypass test mid-stroke. The major difficulty with doing this is that the force developed by the cylinder has to be mechanically resisted, which in the case of large diameter, high-pressure cylinders is impractical.
    However a mid-stroke bypass test can be conducted hydrostatically using the intensification effect. The necessary circuit along with a step-by-step procedure for conducting this test is shown here

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    The next installment from Brendan Casey:

    Hello John,
    In your last few hydraulics bulletins, we've talked about repairing and testing hydraulic cylinders.
    Today I want to explain some of the ways you can increase the service life of your hydraulic cylinders.
    A major cause of reduced service life is damage to the surface of the cylinder rod. Dents and gouges in the rod's hard chrome surface reduces the life of the rod and wiper seals.
    Not only that, it gives dust and other contaminants an easy path into the hydraulic system, increasing the load on the systems filters.
    The potential for damage to cylinder rods and wiper seals is an ever present problem - especially for users of mobile hydraulic equipment.
    One way to minimize this problem is to install a protective shroud or bellows to any cylinders exposed to impact damage. This helps protect the rod's surface from dings and scratches. In abrasive or corrosive environments, it also helps extend rod and wiper seal life and provides an extra barrier to the ingression of contaminants via the cylinder rod.
    That said, the use of a protective shroud is not practical in all cases. So in your next hydraulics bulletin in a few days time, I'll explain an alternative that offers similar life extension benefits.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    Hello John,
    In your last hydraulics bulletin, I explained the benefits of installing a bellows or shroud on a hydraulic cylinder.
    Today I want to talk about alternative rod-surface treatments - to conventional electroplated hard chrome, and the life extension benefits they can offer.
    The first of these is High Velocity Oxygen Fuel (HVOF) which is essentially a metal spraying process. When applied correctly this surface treatment has superior hardness and impact, corrosion and wear resistance to hard chrome. This means HVOF cylinder rods typically last longer in abrasive or corrosive environments than their hard chrome counterparts.
    Black nitride is another alternative. It's an atmospheric furnace treatment developed and patented in the early 1980's. It combines the high surface hardness and corrosion resistance of nitriding with additional corrosion resistance gained by oxidation.
    When it comes to its performance, I've heard mixed reports. One client reports three times the service life in corrosive environments when compared with conventional hard chrome.
    While another client trialled black nitride on salt trucks and found the rods started flaking after one year's service.
    I've also heard one report of long, small-diameter black nitride rods snapping under load.
    A third alternative is nickel under chrome. In the USA, Prince Hydraulics markets this rod treatment as Royal Plate. And this nickel/chrome coating is also offered by Socatri of France.
    Although I've had no direct experience with nickel/chrome plating, according to reports from a reliable source, its corrosion resistance is superior to conventional hard chrome and black nitride - but not as good as hard chrome plated stainless steel.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    Traps! More from Brendan Casey

    John,

    Clause 5.4.6.5.1 a) of ISO 4413 "Hydraulic fluid power - General rules and safety
    requirements for systems and their components" states: "hose assemblies shall be
    constructed from hoses that have not been previously used in operation as part of
    another hose assembly and that fulfil all performance and marking requirements
    given in appropriate standards;"

    This means squeezing a new end onto a hydraulic hose that has previously been in
    service contravenes ISO 4413. In the majority of cases, the practical implications
    of this directive are not burdensome. After all, in most situations, the hose end
    outlasts the hose itself.

    But one situation where this directive can be a 'fly in the ointment' for some
    hydraulics users is in the case of umbilical length hoses. For example, say a 15
    meter length of 2" multi-spiral hose sustains external damage within 5 meters of
    its end, but the rest of the hose is otherwise in serviceable condition. In such
    situations, due to the high cost of the hose, an economical solution may be to cut
    5 meters off the original hose, squeeze a new end onto it and join a new 5 meter
    length to it. You may have seen this done. I know I have. But it's not consistent
    with good practice--or compliance with the Standard.

    Nothing is a problem until it becomes a problem. Meaning in the above scenario, so
    long as the re-terminated hose doesn't blow its new end off, all is good. But if
    the end blows off causing personal injury or significant oil spill, and a
    Standard-waving safety inspector comes around, then it IS a problem. In most
    jurisdictions, Standards such as ISO 4413 are not L-A-W. But they will be
    referenced should a civil claim eventuate. Which means re-terminating a hydraulic
    hose can turn out to be a very costly mistake.



    Yours for better hydraulics knowledge,

    Brendan Casey

    The Industrial Hydraulics Handbook
    Agtronix - the home of the Weedswiper

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    Re: Hydraulics myths

    Quote Originally Posted by john maddock View Post
    Traps! More from Brendan Casey

    John,

    Clause 5.4.6.5.1 a) of ISO 4413 "Hydraulic fluid power - General rules and safety
    requirements for systems and their components" states: "hose assemblies shall be
    constructed from hoses that have not been previously used in operation as part of
    another hose assembly and that fulfil all performance and marking requirements
    given in appropriate standards;"

    This means squeezing a new end onto a hydraulic hose that has previously been in
    service contravenes ISO 4413. In the majority of cases, the practical implications
    of this directive are not burdensome. After all, in most situations, the hose end
    outlasts the hose itself.

    But one situation where this directive can be a 'fly in the ointment' for some
    hydraulics users is in the case of umbilical length hoses. For example, say a 15
    meter length of 2" multi-spiral hose sustains external damage within 5 meters of
    its end, but the rest of the hose is otherwise in serviceable condition. In such
    situations, due to the high cost of the hose, an economical solution may be to cut
    5 meters off the original hose, squeeze a new end onto it and join a new 5 meter
    length to it. You may have seen this done. I know I have. But it's not consistent
    with good practice--or compliance with the Standard.

    Nothing is a problem until it becomes a problem. Meaning in the above scenario, so
    long as the re-terminated hose doesn't blow its new end off, all is good. But if
    the end blows off causing personal injury or significant oil spill, and a
    Standard-waving safety inspector comes around, then it IS a problem. In most
    jurisdictions, Standards such as ISO 4413 are not L-A-W. But they will be
    referenced should a civil claim eventuate. Which means re-terminating a hydraulic
    hose can turn out to be a very costly mistake.



    Yours for better hydraulics knowledge,

    Brendan Casey

    The Industrial Hydraulics Handbook

    Hi John,

    I expect Tasmanian hose assemblers are the same as ours here where crimping new ends on old hoses has become a no-no? Been like that now for maybe 10 years at least now I expect.

    Ironically I steered away from one brand of hose and ends which had the tendency to blow crimps off new hose, let alone used! the design used a particularly short sleeve on the crimp making it compact, but in service especially on 1" hoses such as flail hedge-trimmers it was common for the crimp to separate from the hose just from lack of actual hose crimped to the fitting.
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    Re: Hydraulics myths

    More from Brendan Casey:


    Hello John,
    In your last hydraulics bulletin, we discussed the cylinder life extension benefits presented by alternative rod surface treatments.
    Today I want to talk about a major cause of hydraulic cylinder failure and how to prevent it. Bent rods are a common cause of rod seal failure and therefore, cylinder failure. Bending of cylinder rods can be caused by:
    - Insufficient rod diameter
    - Insufficient strength of the rod material
    - Improper cylinder mounting arrangement
    - Or a combination of all three
    Once the rod bends, excessive load is placed on the rod seal resulting in premature failure of the seal.
    If a rod is bent, then it's wise to check actual rod loading against permissible rod loading based on the cylinder's mounting arrangement, the diameter of the rod and the mechanical properties of the rod material.
    The procedure for doing this is explained in detail on pages 58 and 59 of Industrial Hydraulic Control
    If actual rod load exceeds permissible load then a new rod should be manufactured from higher strength material and/or the rod diameter increased to prevent the rod from bending in service.
    In your next hydraulics bulletin in a few days time, I'll reveal three more common causes of hydraulic cylinder failure.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  20. #20
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    Re: Hydraulics myths

    John
    Keep these tips coming - a lot of them are common sense once the thought process has been initiated.

  21. #21
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    Re: Hydraulics myths

    Quote Originally Posted by Ironhead View Post
    John
    Keep these tips coming - a lot of them are common sense once the thought process has been initiated.
    Happy to Ironhead, although I expect they'll stop in due course - unless Brendan Casey is reading this and writes a few extra just for BFFers!

    I have to admit the first one still stresses my brain cells.

    JV
    Agtronix - the home of the Weedswiper

  22. #22
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    Re: Hydraulics myths

    The next tip from Brendan Casey:

    Hello John,
    In your last hydraulics bulletin, we talked about how to check cylinder rod buckling loads and stop your cylinder rods from bending - to prevent premature failure of the cylinder.
    Today I want to share with you, three other common causes of hydraulic cylinder failure:
    1. Ballooned Tubes
    Ballooning of the cylinder tube is usually caused by excessive honing or insufficient wall thickness and/or material strength for the cylinder's operating pressure.
    Once the tube balloons, the correct tolerance between the piston seal and tube wall is lost and high-pressure fluid bypasses the seal. This high velocity fluid can erode the seal and localized heating caused by the pressure drop across the piston reduces seal life.
    2.Insufficient Bearing Area
    If the internal bearing areas in the gland and on the piston are insufficient to carry the side thrust transferred to the cylinder, excessive load is placed on the rod and piston seals. This results in deformation and ultimately premature failure of the seals.
    3. Rod Finish
    The surface finish of the cylinder rod can have a dramatic effect on the life of the rod seal. If the surface roughness is too low seal life can be reduced through inadequate lubrication.
    If the surface roughness is too high, contaminant ingression is increased and an unacceptable level of leakage can result.
    Keep in mind that not all hydraulic cylinders are made equal. So if you have a hydraulic cylinder that suffers from recurring failure, it's likely that modifications to the cylinder are required to break the vicious circle of failure and repair.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  23. #23
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    Re: Hydraulics myths

    More good info from Brendan Casey. Note the link towards the end - might save you a bundle at a critical time.

    Hello John,
    In your last couple of hydraulics bulletins, we've discussed four common causes of premature failure of hydraulic cylinders.
    Today I want to switch gears and talk about the overlooked value of hydraulic schematic diagrams.
    A schematic diagram is a 'road map' of the hydraulic system and to a technician skilled in reading and interpreting hydraulic symbols, is a valuable aid in identifying possible causes of a problem.
    This can save a lot of time and money when troubleshooting hydraulic problems.
    If a schematic diagram is not available, the technician must trace the hydraulic circuit and identify its components in order to isolate possible causes of the problem.
    This can be a time-consuming process, depending on the complexity of the system. Worse still, if the circuit contains a valve manifold, the manifold may have to be removed and dismantled - just to establish what it's supposed to do. Reason being, if the function of a component within a hydraulic system is not known, it can be difficult to discount it as a possible cause of the problem.
    The humble hydraulic symbol eliminates the need to 'reverse engineer' the hydraulic circuit.
    As most hydraulic technicians know, there's usually a better than even chance that a schematic diagram will not be available for the machine they've been called in to troubleshoot. This is unlikely to bother the technician because it is the machine owner who pays for its absence.
    Where do all the hydraulic schematic diagrams go? They get lost or misplaced, they don't get transferred to the new owner when a machine is bought secondhand and in some cases they may not be issued to the machine owner at all. Why? Because generally speaking, hydraulic equipment owners don't place a lot of value on them.
    So if you're responsible for hydraulic equipment and you don't have schematic diagrams for your existing machines, try to obtain them - before you need them. And ensure that you are issued with schematic diagrams for any additional hydraulic machines you acquire.
    And if you'd like to know how to read schematics like a pro, get yourself a copy of this e-book today

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  24. #24
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    Re: Hydraulics myths

    More from Hydraulics warehouse:

    Today I want to deal with a question that I'm often asked by hydraulic equipment users:
    When it comes to the oil's operating temperature - how hot is too hot?
    Heating of hydraulic fluid in operation is caused by inefficiencies. Inefficiencies result in losses of input power, which are converted to heat.
    A hydraulic system's heat load is equal to the total power lost (PL) through inefficiencies and can be expressed as:
    PLtotal = PLpump + PLvalves + PLplumbing + PLactuators
    If the total input power lost to heat is greater than the heat dissipated, the hydraulic system will eventually overheat. Hydraulic fluid temperatures above 180F (82C) damage most seal compounds and accelerate degradation of the oil.
    So while the operation of any hydraulic system at temperatures above 180F (82C) should be avoided, fluid temperature is too high when viscosity falls below the optimum value for the hydraulic system's components.
    This can occur well below 180F (82C), depending on the fluid's viscosity grade (weight).
    To achieve stable fluid temperature, a hydraulic system's capacity to dissipate heat must exceed its inherent heat load.
    For example, a system with continuous input power of 100 kW and an efficiency of 80% needs to be capable of dissipating a heat load of at least 20 kW.
    It's important to note that an increase in heat load or a reduction in a hydraulic system's capacity to dissipate heat will alter the balance between heat load and dissipation.
    As you've probably gathered, there are only two ways to solve overheating problems in hydraulic systems:
    1. Decrease heat load; or
    2. Increase heat dissipation.

    Decreasing heat load is always the preferred option because doing so increases the efficiency of the hydraulic system.
    In your next hydraulic maintenance email in a few days time, I'll explain how to troubleshoot a hydraulic system that's overheating.
    In the meantime, be aware that continuing to operate a hydraulic system when the fluid is over-temperature is similar to operating an internal combustion engine with high coolant temperature.
    Damage is guaranteed.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  25. #25
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    Re: Hydraulics myths

    Overheating hydraulics

    Hello John,
    In your last hydraulics bulletin, we discussed what causes a hydraulic system to overheat.
    Today I want to explain a technique that is very useful when you're troubleshooting a system that's overheating.
    This technique involves using an infrared thermometer - sometimes called a heat gun, to measure the oil's temperature drop across the heat exchanger.
    The heat rejection of the exchanger can then be calculated and when this is expressed as a percentage of input power, it will reveal whether the problem is in the cooling circuit or elsewhere in the system.
    The exact procedure for doing this is explained in detail on pages 103 - 104 of The Hydraulic Troubleshooting Handbook
    Installed cooling capacity typically ranges between 25 and 40 percent of input power. So if a system has a continuous input power of 100 kilowatts and the exchanger is dissipating 26 kilowatts of heat, this means the efficiency of the system has fallen below 74 percent. If the system is overheating, this is a good indication that there is abnormal heat load somewhere in the system.
    On the other hand, if a system has a continuous input power of 100 kilowatts and the exchanger is dissipating 10 kilowatts of heat and the system is overheating, this means that there's a problem somewhere in the cooling circuit or the system does not have enough installed cooling capacity.
    In your next hydraulics bulletin in a few days time, I'll explain how to locate this abnormal heat load.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  26. #26
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    Re: Hydraulics myths

    Another useful trick from Brendan Casey:

    Hello John,
    In your last hydraulics bulletin, I outlined a procedure for determining whether the root cause of an overheating problem lies in the cooling circuit or elsewhere in the hydraulic system. And I invited you to get YOUR copy of The Hydraulic Troubleshooting Handbook, a book that will turn you into a troubleshooting pro.
    If the indications are that the cooling circuit is functioning satisfactorily but the system is overheating - then we need to locate the source of the 'abnormal' heat load.
    When fluid moves from a high pressure zone to a low pressure zone we call this pressure drop.
    When a pressure drop occurs WITHOUT useful work heat is generated. For example, the pressure drop across the ports of a properly functioning motor produces torque at the motor's drive shaft and ultimately useful work.
    On the other hand, the pressure drop across a relief valve doesn't produce any work, so this energy is converted to heat - which is an undesirable heat load on the system.
    Because a pressure drop without useful work creates heat, an infra-red thermometer can often be used as a quick and effective means of locating abnormal heat load.
    For example, if oil is passing over a relief valve, the localized heat generation means this component will be hotter than the rest of the system.
    The correct application and use of an infrared thermometer or heat gun for troubleshooting purposes is explained in detail in chapter 2 of The Hydraulic Troubleshooting Handbook

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  27. #27
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    Re: Hydraulics myths

    Brendan Casey on valves:

    Hello John,
    In your last hydraulics bulletin, I explained how an infrared thermometer or heat gun is an excellent tool for quickly locating internal leakage in a hydraulic system.
    And I'm going to continue on the topic of leakage today and talk about valve leakage.
    There are two main types of valve designs used in hydraulic systems. Spool-type and poppet-type.
    In a spool design, a spool is positioned in its bore to connect the various ports in the valve. The most common type of spool valve we're all familiar with is the directional control valve.
    Because radial clearance is required for the spool to slide in its bore, this valve design in not leakless. To say this another way, even when a port in a spool valve is closed off - a small amount of leakage is possible and should be expected.
    In a poppet design, the valve 'poppet' closes against a seat. This design is generally considered leakless. That is, if the valve is closed and the poppet and its seat are in good condition - there is no leakage across the valve's ports.
    BUT there's an important exception to this rule you should be aware of. Slip-in cartridge valves, also called logic elements are a type of poppet valve commonly found in today's hydraulic systems.
    Even though a logic element can be configured for flow in two directions, it is only 'leakless' in one direction.
    To understand why, read pages 138-139 of Industrial Hydraulic Control

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  28. #28
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    Re: Hydraulics myths

    To coin a phrase: it's complicated!

    Brendan Casey explains:

    Hello John,
    In your last hydraulics bulletin, I talked about the leakage characteristics of spool-type and poppet-type valves.
    Still on the topic of leakage, today I'm going to explain the potential pitfalls when measuring case leakage from a hydrostatic transmission.
    A hydrostatic transmission consists of a variable-displacement pump and a fixed or variable displacement motor, operating together in a closed circuit.
    In a closed circuit, fluid from the motor outlet flows directly to the pump inlet, without returning to the tank.
    Because the pump and motor leak internally, which allows fluid to escape from the loop and drain back to the tank, a fixed-displacement pump called a charge pump is used to ensure that the loop remains full of fluid during normal operation.
    In practice, the charge pump not only keeps the loop full of fluid, it pressurizes the loop to between 110 and 360 PSI, depending on the transmission manufacturer.
    (If I've lost you at this point, read or re-read pages 121 to 124 of The Hydraulic Troubleshooting Handbook)
    When a pump or motor is worn or damaged, internal leakage increases and therefore the flow available to do useful work decreases.
    This means that the condition of a pump or motor can be determined by measuring the flow from its case drain line (internal leakage) and expressing it as a percentage of its design flow.
    However, using case drain flows to determine the condition of the components of a hydrostatic transmission, without a thorough understanding of the circuit in question, can result in incorrect conclusions and the costly change-out of serviceable components.
    In most transmissions, the charge pump relief valve vents into the case of either the pump or the motor.
    This means if the motor case drain flushes through the transmission pump case to tank, you would expect to see the flow meter in the transmission pump case drain line reading design charge pump flow. Here's why:
    Say charge pump flow is 10 GPM, of which 4 GPM is leaking out of the loop through the motor's internals (case drain) and 2 GPM is leaking out of the loop through the pump's internals. The balance of 4 GPM must therefore be going over the charge relief - but still ends up in either the pump or motor case, depending on the location of the charge relief valve.
    In a circuit where the motor case drain flushes through the transmission pump case to tank, you would expect to see the flow meter in the transmission pump case drain line reading the sum of these three flows (10 GPM).
    So before any meaningful conclusions can be drawn, the case in which the charge pump relief is venting (motor or pump) must be determined and the two case drain lines (motor and pump) must be isolated from each other.
    In your next hydraulics bulletin in a few days time, I'll reveal another component of most hydrostatic transmissions that complicates this issue further.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  29. #29
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    Re: Hydraulics myths

    More from Brendan on hydrostatic transmissions:

    Hello John,
    In your last hydraulics bulletin, I explained the pitfalls to look out for when assessing the condition of a hydrostatic transmission by measuring its case drain flow.
    There's another component present in most hydrostatic transmissions that complicates this issue further: the flushing valve.
    A closed circuit flushing valve (also called a transmission valve or replenishing valve or purge valve) usually comprises a pilot operated directional valve and a low pressure relief valve.
    When the hydrostatic transmission is in neutral, the directional valve is centered and the gallery to the low pressure relief valve is blocked.
    When the transmission is operated in either forward or reverse, the high pressure side of the loop pilots the directional valve. This opens the low pressure side of the loop to the relief valve gallery.
    In a closed circuit, fluid from the motor outlet flows directly to the pump inlet. This means that apart from losses through internal leakage, which are made up by the charge pump, the same fluid circulates continuously between pump and motor. If the transmission is heavily loaded, the fluid circulating in the loop can overheat.
    The function of the flushing valve is to positively exchange the fluid in the loop with that in the reservoir.
    You can watch a 2-minute simulation video which explains how it does this, here
    When the hydrostatic transmission is in neutral, the flushing valve has no function and charge pressure is controlled by the charge relief valve in the transmission pump.
    When the transmission is operated in either forward or reverse, the flushing valve operates so that charge pressure in the low pressure side of the loop is controlled by the relief valve incorporated in the flushing valve. This relief valve is set around 30 psi lower than the charge pump relief valve located in the transmission pump.
    The effect of this is that cool fluid drawn from the reservoir by the charge pump, charges the low pressure side of the loop through the check valve located close to the transmission pump inlet. The volume of hot fluid leaving the motor outlet, that is not required to maintain charge pressure in the low pressure side of the loop, vents across the flushing valve relief and back to tank, often via the motor and/or pump case.
    So if a flushing valve is fitted to a transmission, it acts as the charge pump relief valve once the transmission is operated in forward or reverse. So if the flushing valve vents into the case of the motor, then it is possible to determine the condition of the pump by measuring its case drain flow, but not the motor.
    If the flushing valve vents into the case of pump, then it is possible to determine the condition of the motor by measuring its case drain flow, but not the pump.
    This reinforces the point that using case drain flows to determine the condition of the components of a hydrostatic transmission, without a thorough understanding of the circuit in question, can result in incorrect conclusions and the costly change-out of serviceable components.
    In your next hydraulics bulletin, I'll explain another important concept to keep in mind when testing hydrostatic transmissions. Look out for it in a few days time.

    Yours for better hydraulics knowledge,
    Brendan Casey
    Agtronix - the home of the Weedswiper

  30. #30
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    Re: Hydraulics myths

    An experiment for you:

    John,
    When a conventional hydraulic tank is designed and constructed there's a lot of things to consider. One of them is to ensure an air-sucking vortex (like that you see when water goes down a drain) can not develop at the pump intake line penetration. The following will ensure that it doesn't:
    --Locate the intake penetration at least five times its inside diameter from the nearest reservoir wall, and no less than half its inside diameter, (but at least 100 mm or 4"), off the bottom.
    --Ensure the intake penetration always remains submerged by at least twice its inside diameter.
    --Size the intake line so that fluid velocity is no more than 1.2 m/sec (4 ft/sec), and preferably slower.
    --Terminate the intake penetration inside the tank with a bell-mouthed adaptor or flared tube. This reduces fluid velocity at the point of entry. It also tends to minimize turbulence and this results in quieter pump operation.
    --On flooded inlets, install a vertical baffle along the intake penetration's center line. To check the effectiveness of this technique, pull the plug on a sink of water, wait for the vortex to develop, and then watch what happens when you insert your experimental baffle!

    Yours for better hydraulics knowledge,
    Brendan Casey
    The Industrial Hydraulics Handbook
    Agtronix - the home of the Weedswiper

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