Curcuit problem

[Lowbands]

Hi,
I am trying to control a double acting cylinder to apply a series of loads on to a test part. ie 10bar, 20bar 30 bar and so on up to 110 bar and then back down again to zero. I am hoping to use proportional relief valves to apply the load on the ramp up but am a little stuck on how I can control the load on the way back down. I cant rely on the test peice still exerting a pressure on the actuator as it could deform. Can anyone help!

 

[Ken Cunningham]

Are you trying to apply force in one direction only,

If you ramp up pressure on one side of the cylinder piston the pressure is relative only to the resistance of the test piece to withstand that force. So what im trying to point out is that when you start to relive the pressure from that side of the piston it will only push back with the force that has built up from any spring affect from deformation. You could install a needle valve in the pressure line to relieve it slowly in steps.

Or are you applying force in two directions, pulling and pushing on it?

 

[KennyV]

Is this an attended or an unattended ramp up down test?
If attended, monitoring a simple pressure gage in the system calibrated to the applied load.

 

[Lowbands]

Hi again.
The test is unatended and PC controled. There is only force applied in one direction. The problem is weather or not the pressure in the actuator can be ramped back down in a controlled way using the force or deflection in the component.

 

[J_J]

Hi again.
The test is unatended and PC controled. There is only force applied in one direction. The problem is weather or not the pressure in the actuator can be ramped back down in a controlled way using the force or deflection in the component.

You could put a check valve in the extend port that will let fluid flow in, and check/block the fluid coming out, and parallel the check valve with a needle valve, so the push back fluid will have to go through a needle valve, and adjust to suit your purpose.




https://www.surpluscenter.com/item.asp?UID=2009080610381774&item=9-4218-A&catname=hydraulic

 

[tommu56]

Why not use an I to P converter that current and the pressure is proportional.

then you can ramp up and down the pressure as needed.

HydraForce Hydraulic Cartridge Valves and Electronic Control Systems for Mobile Off-Highway and Industrial Equipment

we use I to P pneumatic controls all the time.

the signal is usually 4 -20 ma or 1 to 10 volts the current is more resistive to induced voltage problems

tom

 

[fluidpower1]

A Low Tech way would be to use a Pilot Operated Pressure Reducing Valve set at the maximum pressure required. Use a number of N.C. 2-Way Solenoid Operated Directional Control Valves Inlet port to Block the External Pilot Port of the Reducing Valves. Connect the 2-Way valves Outlet port to a Direct Acting Remote Relief Valve set at the different required lower pressures.

Energizing any Solenoid will automatically set the Reducing Valve to the pressure set on the Remote Relief Valves while the Reducing Valve will maintain maximum required test pressure with all the Solenoids off.

I show circuits for Reducing valves in a training book I use to teach circuit design here:

Fluid Power Ebook Edition 2

However the section with Reducing Valve Circuits is not on the site yet. They have been putting up a section every two or three weeks so far so that section should be up soon.

Fluid Power Circuits Explained is a book I wrote to teach Mechanical and Electrical Engineers and Maintenance persons about circuit design after they had gone through the Basic book also presented at the Hydraulics & Pneumtics site.

A third book on "Trouble Shoting Hydraulic Circuits" will be presented later on. It uses a different approach than most of the Hydraulic Trouble Shooting books and stresses how working circuits should perform and gives the different failure modes seen in most circuit mal-functions for a given circuit.

This Web Site has brochures for all three books here:
Fluid Power engineering - Advanced Fluid Power Text
Scroll down to almost the end to see download links.