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Frequently Asked Questions
Some common hydraulic questions and their answers. If you have anything to add or a more complicated question please contact us.
Link to Technical FAQs at Prince Manufacturing Corporation.
Pump and Motor
What is the difference between a pump and a motor?
A pump converts rotational force on its shaft into pressurized oil to supply hydraulic components. Example: electric or gas motor turns pump shaft, pump supplies oil to a cylinder. Pumps generally have large suction port and a smaller pressure port.
A hydraulic motor converts pressurized oil to one of its ports into rotational force on its shaft. Motors generally have equal size ports.
What pump do I need for my application?
First, determine if you have an open or closed center system. Next, determine how much flow (GPM) you need. Next, how many components (cylinders, motors) are going to be powered by the pump. You also need the size of the mounting flange, the type and size of shaft, the type and size of ports and the direction of rotation when facing the shaft.
Cylinder
What cylinder do I need for my hydraulic system?
First, do you need a single or double acting cylinder? Next, what is the pin to pin distance when extended and retracted. Also, how much force do you need to move the load, do you need it to move in a certain amount of time and how is the cylinder mounted.
What's the difference between a single and a double acting cylinder?
A single acting cylinder only provides force one way (most snow plow and telescopic cylinders are single acting). A double acting cylinder provides force when extending and retracting.
How do I measure a cylinder?
Measure the pin to pin length when the cylinder is fully extended and fully retracted, measure the diameter of the rod, the bore of the cylinder will typically measure 1/4" - 1/2" less than the outer diameter of the barrel, also determine the type and size of the ports. Finally, determine the type and size of the end mounts.
How much force does my cylinder have?
Force is determined by multiplying the area of the piston by the pressure (PSI).
(r2 x p x PSI)
How does a displacement cylinder work?
In a displacement (single acting) cylinder the rod is extended by flowing pressurized oil behind the rod, which forces the rod out of the barrel like a piston. Once the pressure is released, the load on the cylinder retracts the rod. The diameter of the rod is the effective piston area.
What model cylinder do I need for my application?
See "How do I measure a cylinder?" Once you have that information click the above link for cylinders and choose one that matches your specifications.
Systems
What components do I need to build a logsplitter or a hydraulic power unit?
Start with the cylinder or motor you want to drive, select a pump with the appropriate flow and pressure; select a motor or engine with enough HP to drive the pump to the required pressure; then select a directional valve, pressure relief valve, reservoir, filter, hoses and fittings etc. to assemble the power unit.
Where should an oil filter go?
An oil filter can be mounted on the suction line or pressure line. We recommend mounting on the return line so you do not restrict your suction line, and so a finer filter can be used.
Do I have an open or closed center system?
On an open center system oil can flow through the valve when it is in neutral. These systems normally use gear pumps or vane pumps. On a closed center system the oil flow will be blocked when the valve is in neutral. These systems normally use piston pumps.
What size reservoir tank should I use?
Generally you need a minimum of one minute of oil in your tank. This is determined by the GPM of your pump. Constantly loaded systems, especially hydraulic motors, may require a larger tank or a heat exchanger to prevent overheating.
Misc.
How do I determine fitting or port size and type?
Measure the diameter of the threads, determine if the fitting is a tapered thread (NPT) or a straight thread (SAE, JIC, ORB), and if it is angled or it swivels.
What oil should I use?
Use the manufacturer's recommended oil type. If you do not know what is recommended use a quality hydraulic oil, remember to use lighter oil in the winter and heavier oil in the summer.
How often should I change my oil and filter?
The filter should be changed every 6 months to a year, depending on use. The oil should be changed if it starts to turn milky (due to water contamination), starts to break down (overheating, varnish deposits), or smells like it has burned.
How do I measure a seal?
The inner diameter (I.D.), outer diameter (O.D.), and height are the most common ways to measure a seal. You can also take these measurements from the cavity where the seal is located.
How do I measure a hose?
Measure the overall length of the hose, including fittings. Also, determine the type and size of fittings. The outer diameter is usually 1/4" - 3/8" larger than the nominal size.
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