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Solving Hydraulic System Piston-Pump Problems ben lee

In hydraulic systems, a cracked piston-pump or motor housing is something that is considerably more common than many engineers imagine.

Usually this situation is caused by a case-drain line that is either restricted or blocked; sometimes the case drain line is not even attached. In this particular scenario, the pump or motor housing is transformed into a pressure vessel, something that it’s not designed nor intended to be. In fact it’s likely to just go bang! In addition blocked filters can also restrict the drain line and can also lead to cracked housing.

However, you wouldn’t be held to blame for thinking that a cracked hydraulic piston housing would be caused by a failure in the pumps rotating group. Although, in reality, this is something that will rarely occur.

Connecting a flowmeter to measure the internal leakage of a pump or motor case drain line can achieve the same effects if you omit to set the loading valve to the open position. The housing will fail very shortly after starting-up. It’s not a joke, it has happened before and it’s not something that you will want to have to deal with.

Hydraulic systems don’t work well with too much pressure

If there is leakage that surges inside the pump or motor case, and the filter will not allow it to escape, the pressure can be far too much for the housing – resulting in a crack. It may even blow out its seal. Even if this doesn’t happen, there is likely to be some form of mechanical damage from the high pressure.

There are a few issues with pressure, not just cracking but these results can occur too:

·         When there is high case pressure, there’s likely to be excessive load on the shaft seal lip. This can lead to a groove wearing in the shaft and then leakage occurring. However, if the pressure is very high then it’s more likely that there will just be complete failure, without oil there will be inadequate lubrication and it will all go horribly wrong.

·         The piston-ball and the slipper pad socket will be affected by high pressure on axial piston pumps. The slipper may even separate from the piston, the failure resulting from this can be catastrophic.

It’s very important to install the correct type of filter in hydraulic systems. For example, putting a depth filter on a drain line would not be a good idea and is not recommended. 

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