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.

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.

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.

The inner diameter (I.D.), outer diameter (O.D.), and height are the most common ways to measure a seal. It’s best to take these measurements from the cavity where the seal is located and the shaft which goes through it.

Long term wear: If a pump has thousands of hours of reliable work behind it, it may just wear out. The seals get hard, critical surfaces get worn down, bearings wear out. The symptoms will be gradually decreasing power, & increasing leakage.

Contamination: Sometimes catastrophic pump failure, abrasive dust from the air breathing in & out of the reservoir, rust particles from the inside of the tank when it sits unused, and wear particles from the pump and other components of the system are all sources of contamination.

Cavitation or Aeration: Cavitation is the “starvation” of incoming oil to the pump inlet. The pump wants to pull in more oil than the line from the tank will allow, due to a too-small or restricted suction hose, or to turning the shaft too fast.

Overheating: A hydraulic system produces heat and the oil absorbs it. This can cause seals to get hardened and start to leak, hoses to lose flexibility and crack, and oils to get too thin to lubricate moving metal parts.

The filter should be changed when the pressure drop through it reaches 10 – 15 PSI. Lacking an indicator, the rule of thumb is 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. The oil in a hydraulic system is usually good for a long time, perhaps years, because it usually isn’t exposed to burning heat like oil in an engine. It’s much more important to change the filter. Sending an oil sample to your oil supplier is the best way to tell if your oil is contaminated or worn out.