This page provides answers to frequently asked questions regarding; troubleshooting basic hydraulic systems, basic installation/plumbing diagrams, basics on functionality of our control valves (manual and solenoid operated) and directions for identifying our products. Troubleshooting Basics

1) All hydraulic valves must be properly installed into the hydraulic system to prevent personal injury and/or property damage. Further, the improper servicing of a valve may result in personal injury and/or property damage. Please read and understand all catalog and service information before starting. As with all mechanical work the proper tools, knowledge, and safety equipment are required. Always wear safety glasses.
2) Make sure all pressure has been relieved in the hydraulic lines before installing or servicing a hydraulic valve. Warning: escaping hydraulic fluid under pressure can have sufficient force to penetrate skin, causing serious personal injury. Do not use your hand to check for hydraulic leaks.
3) Before installing or servicing a hydraulic component make sure all weight has been removed from the cylinders or motors before disconnecting hydraulic lines. Warning: disconnecting the hydraulic lines while the cylinder or motor is under load may result in the unexpected rapid movement of machine resulting in serious personal injury.
4) DO NOT exceed the operating specifications for pressure, flow or temperature. All hydraulic systems require a means to limit the maximum pressure. This requires either a pressure relief valve in the system or a pump that has pressure compensation. Warning: overpressure may cause sudden and unexpected failure of a component in the hydraulic system resulting in serious personal injury. Always use a gauge when adjusting a relief valve.

Q: What size does my hydraulic reservoir need to be?
A: As a general rule of thumb your hydraulic reservoir in gallons should equal the pump output in gallons per minute.

Q: How do I figure out what size my Prince PTO pump is?
A: You can find out what PTO pump you have by measuring the center section of the PTO and knowing if it is a 6 tooth (540 rpm) or a 21 tooth (1000 rpm) drive shaft. Based on the center section width and the drive shaft, you can determine what Prince model # it is you have. Click here to view Prince PTO dimensional data and specifications.

Q: What is a closed center or open center valve?
A: Open center refers to valves that allow oil to circulate at low pressure through the valve and back to the tank or reservoir when the valve is in the neutral position. Open center systems are normally used with a gear pumps…aka…if the engine is running, it is pumping oil. Closed center refers to valves that do not allow oil to flow through the valve when the spools are in the neutral position. The flow path is dead headed at the valve. Closed center systems are normally used with piston pumps or pressure compensated pumps.

Q: I just bought a new Prince directional control valve and it won’t make my cylinder extend or retract. What is wrong with the valve?
A: Keep in mind that directional control valves work much like a switch, which simply redirects the hydraulic oil flow path. If the oil is getting to the inlet, not going over relief and has a path to tank, there’s not much that can go wrong with the valve.

Here are some common items to check if your valve doesn’t have any pressure or nothing happens when you move the handle are as follows:

• Always make sure the valve is hooked up properly.
• Are there any other valves or tees in the system?
• Always follow all potential flow paths.
• Is there another path the oil can take before it gets to our valve?
• Is there a tee in the line before our valve? Is there air in the system or the oil frothy?
• A low oil level in the reservoir or an undersized oil reservoir can cause this; remember the general rule, 1 gallon of reservoir to 1 gpm of pump flow.
• Is the oil bypassing, going around the cylinder piston seal or bypassing in the motor?
• Is the pump producing any flow at the required pressure? The flow in worn pumps often decreases or is zero as the pressure increases.
• Is there a line hooked up to the outlet of the valve going back to tank? If you are using power beyond you must have a line from the outlet of the valve connected to the tank and a line from the power beyond to the downstream valve.
• Check the quick disconnects in the system if there are any, make sure they are properly connected.

Q: I just put a Prince control valve on and it’s leaking out the back of the valve. What went wrong?
A: There is a very good chance that the outlet line (return to tank line) has been pressurized. Just one tank line spike, over 300 psi, can cause the valve to leak at either the handle or the spool end cap.

Q: I have a Prince product, how do I identify what the model # is?
A: The 1st thing you need to do is determine if you have a Prince hydraulic cylinder, valve, pump, or motor.

Prince typically pin stamps directly on the product or attaches a tag with the model #, date of manufacture, and a serial # or some combination that will include the model #.

Cylinder: On the cylinder tube approximately 90 degrees to the extend port (base end of the cylinder), in a counter clock wise position you should be able to find the pin stamp. Do look closely, depending on the paint thickness or layers of paint it may be difficult to see (you may have to use a flash light or a wire brush to remove some of the paint).

Pumps: On the SP series pumps, this information will be pin stamped on the body of the pump. These are aluminum bodies, so it is usually easy to find the pin stamping.

Aluminum PTO Pump: On the aluminum PTO Pump you will find the pin stamping on the body of the PTO. Keep in mind that depending on the paint, it maybe difficult to find, so look closely, it is there.

Cast Iron PTO Pump: On the cast iron PTO Pump you will find a tag, it is attached to the opposite side of the torque arm mounting area.

Motors: With the motor shaft facing you and the ports up, you will find the tag on the right side of the port pad.

Valves: Prince has a few locations where valves will get pin stamped. Prince typically pin stamps the model # and date of manufacture. You will also find casting #’s (C-XXX or HCI-PRINCE) on the valves, so if you are not able to find the pin stamping, this will give you a start in identifying what valve series you have. Please refer to the valve casting # identification section.

Q: Ok, I can’t find the model # on the valve but I did find the casting #. What valve do I have?
A: The below chart will tell you what valve series the casting # is used in. You will still need to determine the other valve attributes such as port size, relief setting, and others. You can find additional information on each of the below valve series by referring to the specific catalog pages or parts manuals.

Q: I have a HC-PTO-1A pump. I am only getting 900 pounds of hydraulic pressure. What do I have to go to get 2000 pounds of pressure out of it. Please let me know.

It is important to note that a gear pump generates flow. It is the other parts of the system that resist flow, and build up pressure. Therefore, it is important to look over the entire system when investigating a pressure related problem.

Some common items to check:

1) Check oil levels. Low oil levels can introduce air into the system, causing many problems, including loss of flow and/or pressure.

2) Is the hydraulic reservoir large enough for the PTO gpm output? It is important to insure the correct amount of reservoir capacity to avoid problems. A basic rule of thumb is to get at least 1 gallon of reservoir capacity per 1 GPM of pump capacity. (i.e. 21 gpm pump output = 21 gal. or larger reservoir.)

3) Is the pump functioning properly? The proper way to check a pump output is with a flow meter, not a pressure gauge. If the pump is not producing the correct flow, it may be damaged, and require replacement. (See: What kinds of things can cause a pump to fail.)

4) Is the system Plumbed properly? Is the oil passing around, rather than through its intended path? Is the oil passing over a relief set too low?

5) Is the system working properly with the currently generated pressure? Many hydraulic systems do not use the full extent of rated pressure unless at full load. If you do not have enough load on the system, you will not generate a very high pressure.

Please refer to the PTO Parts Manual to ensure the pump is plumbed properly. You can visit PTO Pumps Page and select Parts Manual to down load or print a copy of the manual.

Q: What are the most common things apart from pressure or speed that can cause a pump to fail?

A: The most common things that cause a pump to fail fall into three categories; Cavitation, Contamination, and Heat.

Cavitation: This is caused by a lack of oil flowing into the inlet port. It will damage the pump, and reduce flow. If you see foamy oil, it is a good indication of cavitation. Increasing the size of the inlet line or reducing flow can help with cavitation problems. Removing any elbows, bends, or filters on the inlet line can also help. Lastly, making sure that the oil reservoir is above the pump may also be beneficial.

Contamination: Contamination will not only cause damage to the pump, but may also plug valves, reliefs, etc. in the system. It is important to have the proper filtration in the system, including changing filters regularly.

Heat: Any Hydraulic system will generate heat. It is important to deal with that heat so that the oil temperature does not rise high enough to cause damage to seals, valves, etc. Having a properly sized oil reservoir (or oil cooler if necessary) is important in order to avoid excessive heat buildup in the system.

Lastly, make sure to refer to your manual for the proper pressure/speed limits. Exceeding those limits will damage a pump, and cause it to fail prematurely.

Q: I’m having trouble with my tractor loader, how can I determine what the problem is?
A: Below is a loader drift test along with some information on loader valve trouble shooting..

FIELD LOADER DRIFT DOWN TESTS
1) Observe all safety precautions. Do not loosen pressurized lines. Stay dear of loaded members of front end loader. Only an experienced hydraulic technician should work on the system.

2) Make sure all fittings are tight and not leaking. Make sure that there is no external leakage from the valve or cylinders.

3) Make sure that there is adequate hydraulic fluid in the reservoir.

4) With the boom and bucket positioned so that there is no pressure in the hydraulic lines, tee a pressure gage into the rod end hydraulic line on the boom cylinders and a second pressure gage into the base end hydraulic line on the boom cylinders.

5) Cycle the boom cylinders to full extend and then full retract a minimum of 5 times to expel any air in the system. The cylinders should be cycled with the engine near maximum rpm. The bucket should not be loaded during cycling.

6) Leakage test for the boom cylinders/spool.

Place a load in the bucket that induces a pressure reading in the boom cylinder base end of approximately 1000 psi. Raise to approximately mid-stroke. After a short period of time note the pressure on the rod end side of the boom cylinders. It should be near zero and not increasing. If it is not near zero or is increasing, oil is leaking past one or both of the boom cylinder piston seals and the cylinders need to be repaired or replaced.

7) If the boom rod end pressure remains low, use a marking pen to mark a line on the cylinder rod 10 inches away from the cylinder gland.
After a set period of time measure the distance between the line and the gland and subtract the distance from 10 to determine how much the cylinder has retracted. Using the boom cylinder bore diameter, calculate the area of the bore in square inches. Take the area of the bore times the number of inches the cylinder has retracted and divide this product by the time between measurements to determine the leakage rate per cylinder in ins/min. Since there are two cylinders, take this number times two for the leakage rate of the boom spool of the valve. Contact the factory to see if this rate exceeds the allowable rate.

8) Leakage test for the bucket cylinders/spool.

With the boom and bucket positioned so that there is no pressure in the hydraulic lines, tee a pressure gage into the rod end hydraulic line on the bucket cylinders. Cycle the bucket cylinders to full extend and then full retract a minimum of 5 times to expel any air in the system. The cylinders should be cycled with the engine near maximum rpm. The bucket should not be loaded during cycling.

9) With the bucket on the ground, roll the bucket down slightly, pressurizing the base end of the bucket cylinder and reducing the weight on the front tires of the tractor.

After a short period of time note the pressure on the rod end side of the bucket cylinders. It should be near zero and not increasing. If it is not near zero or is increasing, oil is leaking past one or both of the bucket cylinder piston seals and the cylinders need to be repaired or replaced.

10) If the bucket rod end presure remains low check for bucket spool leakage in the valve.

With the bucket lip approximately level and on the ground, place a load in the bucket and raise the boom slightly off the ground. The load should be adjusted so that there is a bucket cylinder rod end pressure reading of approximately 1000 psi. Place a mark on the cylinder rod 1 inch away from the cylinder gland. After a set period of time measure the distance from the gland to the mark and subtract 1 inch to determine how much the cylinder has extended. Using the bucket cylinder rod diameter, calculate the area of the rod in square inches and, using the bucket cylinder bore diameter, calculate the area of the bore then subtract the rod area. Take the result of the subtraction times the number of inches the cylinder has extended and divide this product by the time between measurements to determine the leakage rate per cylinder in in3/min. If there are two cylinders, take this number times two for the leakage rate of the bucket spool of the valve. Contact the factory to see if this rate exceeds the allowable rate.



LOADER VALVE TROUBLE SHOOTING
1) External Leakage
Clean all dirt and oil off the exterior of the valve. Cycle the valve a few times to determine the source of the oil leak.
A. If the external leakage is coming from the ports, remove the fitting, check for any damage to the spot face sealing surface or contamination. Replace fitting sealing washer and torque fitting to proper torque.
B. If external leakage is coming out from the spools on the handle end of the body or is coming out from the spring end caps, replace the spool oring seals as outlined in the valve assembly breakdown.

2) When moving the control lever to move a cylinder, the cylinder moves in the opposite direction before moving in the correct direction.
A. Air in the cylinders. With the bucket unloaded, cycle the cylinders to full extend and to full retract a number of times. This should be done with the engine near maximum rpm.
B. Load check not functioning. With the boom and the bucket on the ground and the engine off, use the handle to move the spools in then out. Remove the load check plug, spring and poppet. Inspect the seat and the poppet for any damage. Inspect for any contamination in the cavity.

3) Loader won't lift the load or is slow.
A. Load exceeds the capacity of loader. Reduce load.
B. Pressure setting of the relief is incorrect. Adjust relief per tractor recommendations.
C. Pump is not functioning correctly.
D. Spools in valve are not being fully shifted — check linkages on joystick.

4) System runs hot.
Check to see if oil is going over relief valve during use of the loader.

5) During use, cylinders become "spongy" or allow some spring like movement.
A. Air in the cylinders. The air can be purged by cycling the cylinders to full extend and to full retract a number of times. This should be done with the engine near maximum rpm and with the bucket unloaded. The reservoir should also be checked to see that there is adequate hydraulic oil.
B.Cavitation. When lowering the boom or rolling out the bucket when it is loaded, the oil supply may not be adequate to keep up with the cylinder movement. The engine may need to be run at a higher rpm or one way restrictors may be needed in the boom base end hydraulic line or the bucket rod end hydraulic line.