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: 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 us a start in identifying what valve series you have. If this is the case you will have to give us a call.

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 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.