Variable flow/volume from a hydraulic constant speed pump

Well, I don't know what all the different types of valves may be called, but the valves in my backhoe controls permit a constant speed pump to be applied at any rate between full-bore and just barely creeping, based on how far the levers are pushed. I'm guessing you need that type of valve, whatever it may be called. The excess flow gets diverted back to the tank, same as when no valve is applied at all.

I think this is what you need.

There is no cheap answer.As you have been told using flow restricters will mean oil getting dumped through the relief valve which will heat the oil very quickly.This in turn will lead to increased wear on the pump and hydraulic motor.Probably the cheapest option is to get rid of the hydraulics and drive it direct from an electric motor through either a variable speed gearbox or a fixed ratio gearbox with a vfd on the motor.This in turn will lead to other problems like how quickly you can stop the rack and how quickly you can reverse the rack in the event of the blade jamming/overloading.It might be better to price an adjustable flow pump.If you gave the size of the pump/flow rate/ pressure etc it would be possible to work out exactly what`s needed.Scrapyards are a good source of hydraulic pumps and there are often variable flow pumps on Ebay. Mark.

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Ted,

Presumably the pump is motor driven? If so and it is three phase, why not drive the moter via an inverter so that you can alter the speed and hence flow rate of the hydraulic oil? If the pump is driven off the main power source for the machine, remove it, fit a three phase motor / inverter set up and off you go.

AWEM

You can insert fixed or adjustable flow regulators in line with the valve's supply, or you can swap out the valve for a "motoring spool" style.

LLoyd

Ted, Variable displacement pumps are available. I had one on a log splitter. They have a swash plate that alters the stroke of the pistons, varying the displacement. This is the basis of a hydrostatic transmission; variable pump, fixed motor.

This is far more efficient that restrictors, and diverting valves.

Bob

Thanks everyone for your most helpful imputs. I do have a swashplate hyd pump on one of my own pieces of equipment. And I vary the oil delivery with a lever.

We are howeverlooking at the simpler options first before we start changing pumps etc. Ive made some progress, the hyd motor drives the rack shaft by chain!!, so we plan to change the chain wheel sizes from whats virtually a 1 to 1 drive to a reduction of about 3 to 1. this will improve the variable range of the spool valve. We will look at using some big motor cycle final chain drive cogs.

the hyd motor shaft is 3/4in and the rack drive shaft is 1.And 1/4.in simple enough to set up. Its Easter here so not a lot can be found in the scrap yards till next week. Any way thanks again for everyones imput. Well keep you all posted. Ted.

Ever heard of Occam's Razor?

As someone else suggested:

-Carl