Closed Center Versus Open Center Hydraulics

hydraulic pumps: fixed versus variableIf you’ve been working with hydraulics for a while, you probably consider a hydraulic system with a variable displacement pump to be more efficient than its fixed displacement counterpart. As a generalization this is true but like most things in hydraulics, it depends. And in the case of a variable-displacement pump, it largely depends on the type of control used and the circuit configuration when the pump is on standby. Consider this question I was asked to adjudicate on recently:

“A competitor of mine states that hydraulic oil gets most of its heat when the system is at rest and just circulating the oil around the system.continue reading »

Why A Start-Up Checklist Is Essential

Hydraulic start-up checklistA new client, a hydraulic repairer, consulted me about the failure of one of their piston pump rebuilds. The pump was not installed by them, but when the failed unit came back for inspection, it was obvious the drive coupling had been hammered onto the pump’s drive shaft.

For the uninitiated, this is a really dumb thing to do. If you ever come across a coupling that is tight on its shaft, do NOT reach for a hammer–reach for the emery paper and get busy with it. And this applies to any piece of rotating equipment, not just a hydraulic pump or motor.… continue reading »

How To Implement Offline Filtration

Filter used on a filter cartA very frustrated member sent me this recently:

“I have done all but beg the company I work for to buy a portable oil filtration caddy but I cant seem to get my point across to them. The company is a government contractor and everything is done on a cost basis at the moment. So it’s cheaper to mix oils today because they got a ‘deal’ on oil, or it’s cheaper to change oil than it is to buy an offline filtration system, or most parts are cheaper than the filtration system, or the worst excuse I’ve been given so far is ‘we have a lot of oil, no need to filter it’!continue reading »