Hydraulic Cylinder - Pump & Controls

So why cant you use a piston pump driven from a variable speed source to control the flow rate or just use an adjustable bypass or pressure regulation system?

Seems to me you are over engineering what should be a simple hydraulic process.

I have calculated I need flow of 0.3 to 30 ml/min to maintain pressure ramp. I didn't think of the pressure regulator. That would work for pressure control but I don't know how I will determine how much water was added to the chamber. I need to calculated the %compression of the ballast. (volume reduction)

If the volume is not all that great, you could use a hand pump. I would draw from a graduated cylinder, mark the level when all the air was purged, and mark the level when final pressure was achieved. This way you can hit your top pressure exactly and stop.

To save some math, you can just top off the graduated cylinder when the air was purged, then the water used is your crush volume.

I need to make an automated system. Graduated cylinder cannot early measure 0.3 ml

How big or small is this vessel and what is the anticipated variances in volume that will come from the pressure change?

At 8000 PSI there will be some vessel expansion and a slight but measurable compressibility effect in the water itself.

http://www.mathworks.com/products/simhydraulics/demos.html?file=/products/demos/shipping/sh/sh_hydraulic_axial_piston_pump.html

Hydraulic axial piston pumps...

Thanks for the hydraulic circuit, Now I know how to move and pressurize under control. but ... I need to know volume measurement. Flow meters won't work at this low flow, so I will need some type of positive displacement cylinder with a distance transducer.

http://www.google.com/patents/US4938054

Cant you use a sensitive transducer system and measure the weight increase of your test cylinder and equate this with volume of water??

I have used these, and the tank is filled 100% with water, no air at all, usually by filling from the bottom up to an exit point you can shut off tightly.

Then a hand operated pump connected to a pressure valve is used to pump in water as you monitor pressure. The pressure rises very steeply in a small tank of proper construction, and you increase to the test pressure and shut of water and watch. If there are leaks, the pressure will fall over time. If the pressure goes up too slowly = air in the tank compressing = it was not empty in the first place. If a lot of water goes in this might show a bad design, the tank shape is expanding with the pressure - this could be bad ends or ??, but usually a pressure vessel has half spherical ends and a round tubular long section. Some vessels are made with concave dished ends.

many companies have them.

one supplier

You can do this with a hydraulic servo cylinder connected to a second (water) cylinder made for water service...stainless steel construction and high pressure seals suitable for water. The position feedback from the hydraulic cylinder is simple and usually can be implemented with a magnetostrictive feedback device which can be built right into the hydraulic cylinder.

This kind of hydraulic servo cylinder is standard fare in the sawmill industry (and many other industries) and can move very precisely, following whatever preprogrammed position/velocity ramp you want.

Of course, you will need a suitable hydraulic servo valve and a closed loop feedback controller. The hydraulic power supply is usually a pressure compensated piston pump backed up with a fairly large accumulator. Again, this is all standard stuff in the sawmill game, where the hydraulic actuators are used to position multi-ton cutting equipment to .001" tolerances at very high speeds.

I've used Delta Computer Systems (www.deltamotion.com) on my equipment. I have no connection with this firm but they have done lots of hydraulic servo control and probably have done similiar things to what you are looking for. They don't do the hydraulics, just the control, but probably can recommend cylinder manufacturers, servo valves and hydraulic power unit fabricators to you.

Hope this helps,

Jon.