Testing Hydrualic Pressure

I put a pressure gauge on my loader to get a better understanding of it's load capacity. It cost about $10.00 plus the cost of a few fittings. It was money well spent. It gives me an understanding of where the load capacity / limit is. Buy one.

Fessman

One comment: A easy way to think about hydraulics is that pumps produce flow but loads produce pressure. Only enough pressure to move a load is developed. Pumps also don't have 100% volumetric efficiency. The volume pumped decreases as pressure increases.

An approach other than measuring is simply to run the curl to the end of its travel and listen for the pressure relief valve to open. If it opens, then there's not a pressure problem unless the relief valve is low. Pressure tests often are taken to adjust relief valves.

Generally a pump that can open its relief valve doesn't have too bad a flow. However, obstructed suction lines and clogged filters will reduce flow.

Checking the general condition of the system would be good. Condition of filters and screen should be known and the oil should not become abnormally hot or frothy during normal work. A diverter valve (if present) should be fully in the auxiliary system position. The loader should not leak-down under load.

If the general system checks out, a relief valve pressure test will test for pump/relief valve condition. A manual would describe the procedure. If pressure tests low, the pump may be worn but the relief valve may be faulty. Most relief valves are adjusted by placing shims behind a spring. If adding shims doesn't bring up the pressure, the pump likely is at fault.

In terms of theory, a relief valve test can be thought of as applying an infinite load to the system to force the relief valve open. A system never has more pressure than is required to move a load. Oil is pumped continuously in an open centred system, and line pressures are around 100 lbs. when noting is operated. The 100 lbs. is the load of the lines and apertures. Lifting anything requires increased pressure and pressure is the only thing that moves a load. Heavy loads develop more pressure than light ones.

Pumps are often thought of in terms of their ability to withstand, rather than to develop pressure. Vane pumps typically wear well but fail catastrophically. The performance gear pumps typically declines gradually over their service lives. However, all type pumps in acceptable condition should be capable of withstanding pressures quite a bit higher than the relief valve pressure (which limits the maximum load in a system). If a vane pump is pumping at all, it’s fairly likely that it would be capable of opening a properly adjusted relief valve unless there were many hours on the pump.