2. Hydraulics For The Long Term
Most Companies Make Very Few Preventive Maintenance Checks Such As:
Oil Level
Filter Condition
Leaks
Pump And Motor Coupling
Most company’s make very few preventive maintenance checks. This is a result of not knowing WHAT to check. When the machine fails, there is little or no information about the system to refer to when troubleshooting.  

3. Forklift Maintenance Checklist
Mobile equipment manufactures will provide you with an overall maintenance checklist. However, there are still very few checks that have to do with the hydraulic system.
Manufactures of Industrial hydraulic systems like paper machines, presses, blow molding etc. do not provide any type of checks like this one. So does this mean that the hydraulic system will never need attention and the pumps and valves will last forever? Of course not. 3

4. How To Improve The Longevity Of Your Hydraulic System
Testing of the pump(s) to determine if the proper volume is being delivered to the system. By making this test regularly the pump can be replaced on a down day and not when it fails and interrupts production.
Checking the accumulators to make sure they are properly pre-charged which is necessary to achieve the desired speed to maintain production.

5. How To Improve The Longevity Of Your Hydraulic System
On any given hydraulic system, there should be some lines that are hot (above 130 degrees), warm ( degrees), and cool or at ambient temperature. By checking the temperature of these lines on a regular basis a component failure can be found before the system fails completely.
One of the main issues in a hydraulic system is leakage. One drop of oil that drips once per second will lose 405 gallons a year. If leakage is occurring there is a reason for it. 5

6. How To Improve The Longevity Of Your Hydraulic System
One of the biggest problems in systems today is that the pressures are out of adjustment which causes excessive force, heat, leakage and wasted electrical energy. You will identify any pressure setting issues and many times correct them during the checks.
Check to verify that the pipe and tubing clamps are properly spaced and are of the proper type.  Make sure that the hoses are properly installed to prevent pre-mature failure and oil loss. 6

7. How To Improve The Longevity Of Your Hydraulic System
Check the condition of the filters if a visual or electrical indicator is available.
Verify that the air and water heat exchangers are operating properly to reduce the oil temperature to an acceptable level. If the oil temperature is above 140 degrees then oil will start breaking down causing sludge and varnish in the system. 7

8. How To Improve The Longevity Of Your Hydraulic System
Check the condition of the breather cap on the reservoir.
Sound checks to determine pump cavitation, aeration or valves bypassing in the system. 8

9. Hydraulic Reliability Checks That Should Be Made On A Regular Scheduled Basis
Record the maximum and minimum pressures in the system.
Max PSI
Min PSI
Here are some typical reliability checks that can be made on a regular scheduled basis.
We can learn a lot from recording the max and min pressures. 1) If a variable displacement pump is used we can record the compensator setting. 2) If a volume accumulator is used in the system, the pressure drop from max to min while the system is operating should not be more than 500 PSI. If the pressure drop is greater, than this can indicate that the accumulator may have a ruptured bladder, is under or overcharged with nitrogen.
In this picture the knob turner strikes again. The gauge shows a maximum compensator pressure of 1800 PSI. The recommended manufactures compensator setting is 1500 PSI and the pressure relief valve 1750 PSI. The high compensator setting resulted in the relief valve by-passing and creating heat. 9

10. Hydraulic Reliability Checks
2. Record the oil temperature in the reservoir. If there is no thermometer or unreadable, use a temperature gun. °F
This oil temperature here is way to hot. Ideal operating temperatures are 100°F - 120°F. Non synthetic hydraulic oil can start breaking down and leaving varnish behind at 140°F. This high heat may be caused by the high compensator setting, a bad relief valve or dirty cooler. 10

11. Hydraulic Reliability Checks
3. Check the relief valve tank line for heat. The tank line should be considerably cooler than the inlet line. °F
The relief valve is a normally closed valve and is usually set 250 – 300 PSI above the compensator. It should only open if the pressure spikes or if the pump compensator fails. This means that the tank line temperature should always be at ambient temperature or at least cooler than the inlet pressure line. In the picture you can see that the relief valve was by-passing as a result of the high compensator setting. A broken spring, contamination, failed o-rings or relief valve set too low will result in by-passing as well. 11

12. Compensator Set Higher Than The Relief Valve
If the compensator is set higher than the relief valve, the pump will constantly deliver its maximum flow because the pressure never reaches the compensator setting. Any excess flow will dump across the relief valve back to tank creating heat.

13. Adjusting The Pressures
Setting a Compensator In a System With a Relief Valve

14. Adjusting The Pressures
Setting a Compensator In a System With a Relief Valve

15. Adjusting The Pressures
Setting a Compensator In a System With a Relief Valve

16. Adjusting The Pressures
Setting a Compensator In a System With a Relief Valve

17. Adjusting The Pressures
Setting a Compensator In a System With a Relief Valve

18. Adjusting The Pressures
Setting a Compensator In a System With a Relief Valve

19. Hydraulic Reliability Checks
4. Check the temperature of the pump suction line and case drain line.
Suction Line °F Case Drain Line °F
Normal by-passing across the case drain for most pumps is 1 – 3 % of its total volume. If the by-passing exceeds 10% of the total pump volume, it should be changed.
Checking the temperature gain from suction to case drain line is a good indicator of the condition of the pump. These pictures show that the pumps case drain line is 37°F hotter than the the suction line. The more the pump wears and the by-passing increases, the temperature of the case drain line will increase. If the temperature gain is more than 20°F the case drain should be ported into a 5 gallon bucket and the by-passing checked. A flow meter can also be installed to check the by-passing. 19

20. Pressure Compensating Piston Pump
Case Drain Line
The case drain line will get hotter the more the pump wears.
Suction Line

21. Checking The Pumps Case Drain Flow
There are two methods of checking case drain flow:
Run the case drain flow into a container of known size and time it

22. Checking The Pumps Case Drain Flow
A flow meter may be permanently installed in the case drain line.

23. Hydraulic Reliability Checks
5. Check the temperature of the accumulator shell for heat.
Top Of Shell °F Bottom Of Shell °F
When an accumulator is pre-charged correctly the lower half or 2/3rds of the shell will be hotter than the top half do too the oil cycling in and out of the shell. The top half of the shell is cooler due to the nitrogen pre-charge. The pictured accumulator shows only a 3°F difference from top to bottom. The accumulator is either undercharged, overcharged or has a ruptured bladder. If you find that the accumulator is indeed the same temperature, and you are experiencing pressure drops more than 500 PSI (refer to check no.1) you should isolate the accumulator, drain the oil from the shell and place a charging rig on the accumulator to verify the condition of the accumulator. 23

24. Checking The Accumulator
Checking the pre-charge with a charging rig.
Bleed Valve
Gas Chuck
First close the accumulator isolation hand valve and open the manual dump. Place the charging rig on the gas valve and screw down the chuck to read the nitrogen pressure. If it is low you can attach the hose to the nitrogen bottle to increase the charge. If it is high, open the bleeder to remove the nitrogen. If you open the bleed valve and oil comes out as shown in the picture, then the bladder has ruptured.
Hose Connection 24

25. Hydraulic Reliability Checks
6. When was the last date the return filter was changed? Check the visual indicator for the filter condition.
The oil that exhaust out of the valves return lines is ported through this filter before returning back to the tank. The element’s condition should be checked regularly with the visual indicator. The element should also be set up to be changed on a regular basis. This schedule can be established by an oil analysis program. If the element plugs up and the inlet pressure reaches the setting of the internal check valve, oil will bypass the element. 25

26. Hydraulic Reliability Checks
7. Check the condition of the breather caps. When was the last time they were changed?
The breather cap filters the air that enters the reservoir. It usually has a rating of 1 – 40 micron. A plugged breather will cause a reduced or zero vacuum condition in the pump suction line resulting in cavitation. 26

27. Hydraulic Reliability Checks
8. Check the oil level in the reservoir. A sight glass is usually mounted on the side of the tank. 27

28. Hydraulic Reliability Checks
9. Check the condition of the heat exchanger. Are the fins clean and is there good air flow?
The return oil from the actuators is ported through this air cooler before returning to the tank. The fins should be cleaned regularly to remove dust, dirt and greasy deposits. A stiff brush or air nozzle can be used for loose dirt removal. Be careful not to bend the fins when cleaning. If the fins are bent use a “comb” for straightening to insure a good flow of air. Use a mild alkaline cleaning solution with a brush for removing solid and greasy deposits.
To clean deposits from the outside of the core, remove the core and tank assembly and plug all openings. Use a mildly organic solution such as Fine Organics 2223 or Keychem Mix 10% of the solution with water and if possible heat to 160 to 180 degrees. Agitating the core will help in removing the contaminants. Ultrasonic equipment is effective in breaking up the deposits. Once a year the piping should be disconnected and either of the above mentioned solutions used to clean the internal tubes. When flushing, circulate the oil in the opposite direction of the normal oil flow. Once cleaning is complete, flush the unit with oil to avoid rust formation on the internal surfaces. The cooler fan should be turned on at approximately F. This is usually done by a temperature switch on the reservoir. 28

29. Hydraulic Reliability Checks
10. Check the condition of the hydraulic hoses. Are any rubbing or over 4-6 feet in length? If so, hose protectors should be placed over the rub points. 29

30. Hydraulic Reliability Checks
11. Check the condition of the pipe clamps and make sure the proper clamps are used. Clamps should be spaced every 5 – 8 feet and within 6” of where the pipe terminates.
Improper Clamping
Proper Clamp 30

31. Hydraulic Reliability
These are just 11 checks that should be made on a regular scheduled basis.
Depending on the hydraulic system, there can be as many as 25 reliability checks.
A Hydraulic System Reliability Checklist should be developed for all your hydraulic systems.
Some hydraulic systems will have multiple relief valves, pumps, accumulators and filters. 31

32. Questions

33. Hydraulic IQ Test How Much Do You Really Know About Hydraulics?
1. Force = _____ x _______
Pressure x Area

34. Hydraulic IQ Test
2. Pascal’s Law states that pressure in a confined body of fluid will act _______ in all directions.
Equaly

35. 3. Power is the ____ at which work is done.
Hydraulic IQ Test
3. Power is the ____ at which work is done.
Rate

36. 4. Pressure in a hydraulic system is caused by a __________ to flow
Hydraulic IQ Test
4. Pressure in a hydraulic system is caused by a __________ to flow
Resistance

37. Hydraulic IQ Test
5. There are six reasons why a valve solenoid can fail. Can you name one?
The plunger can bind or stick when energized
The valve spool may stick due to contamination
Low voltage
High ambient temperature
The valve mounting base isn’t flat
Energizing both solenoids at once

38. Hydraulic IQ Test
6. When a solenoid is checked with an ohmmeter and the reading is less than 50 ohms, what does this mean?
The solenoid is good (answer)
Infinity means the solenoid is open
0 ohms means the solenoid is shorted

39. 7. What five characteristics does the valve symbol below have?
Hydraulic IQ Test
7. What five characteristics does the valve symbol below have?
Normally Closed
Solenoid Actuated
Spring Return
Two Position
Two Way

40. Hydraulic IQ Test
8. Which valve center position would be best to use with a fixed displacement pump?
The tandem center valve in the middle

41. Hydraulic IQ Test
9. If you were replacing the pilot valve on a solenoid controlled hydraulic piloted valve, which center position would be correct?
The float center valve far right

42. Hydraulic IQ Test
10. Which valve is larger?
The symbol on the right

43. Hydraulic IQ Test
11. What two checks would you make to be sure an accumulator used for volume is operating properly?
Observe the pressure gauge
Check the sides for heat

44. Hydraulic IQ Test
12. If no heat is felt on a bladder accumulator, one of two things has happened. They are:
The accumulator is overcharged
The bladder has ruptured

45. Hydraulic IQ Test
The relief valve serves two functions in a hydraulic system with a variable displacement pump.
They are:
Absorb Pressure Spikes
Act as an extreme safety device

46. 14. What is usually the number 1 reason why pumps cavitate?
Hydraulic IQ Test
14. What is usually the number 1 reason why pumps cavitate?
Plugged suction strainer

47. Hydraulic IQ Test
15. True or False: A particle of contamination whose size is the diameter of a human hair is not harmful to a hydraulic system.
False

48. Hydraulic IQ Test
16. What happens to the electric motor current draw when a pump compensates?
Decreases

49. Thank You For Attending!
Copyright, 2012 © GPM Hydraulic Consulting, Inc.