Best valving for hydraulic ram load testing

[IronFish]

I periodically have to run tension and compression tests on slender steel shafts or tendons to loads of say 100 kips. Mostly contractors show up with Enerpac "donut" hollow ram hydraulic cylinders and either hand pumps or electric pumps. These sometimes have a single valve for holding pressure (usually looks like a ball type based on handle throw) or sometimes there will be one or more multi-revolution knobs that make think they are more of a gate type valve. Several issues come up. Often the support for the ram is cribbing on soil that moves during required constant load hold periods (a few minutes) and pressure backs off. More troubling is that the load test specifications usually call for gradually increasing the loads in increments (which usually works fairly well) but also calls for gradually reducing the load in increments which often doesn't work at all. As soon as the operator cracks the valve you loose all your pressure and load (or most) in one fell swoop. I have tried to read up on the web and on Enerpacs site but there a more variations with cryptic descriptions than I can sort out in a timely manner.

Does anyone have experience with a simple to operate valve setup that lets you apply pressure gradually to reach a load, hold it steady (assuming the cribbing cooperates) and then at some point back the pressure off in a controlled manner? Like a coarse valve & fine tune combination. Are there solenoid systems that let you pre-select a pressure that will move to that psi and then adjust to any creep in the cribbing giving you more consistent results?

Anybody have a cheap one for sale?

Thanks,
Jeff

 

[HPost]

Jeff...

Enerpac produce equipment that is more about grunt than finesse. What you currently have is a digital system where you really want a flexible analogue system that will allow you to vary the pressure.

The trouble is that such systems are not cheap. That said, they don't have to cost the earth either, but as always...you will get what you pay for.

You need a proportional pressure reducing valve that you can use to vary the pressure. This could be controlled relatively easily with a very simple controller (potentiometer).

Building on that, you could apply a PLC or PC based controller that could be used to run an automated system that could be set running and then left to get on with it.

None of what you need to do is going to be cheap, but it could be cost effective for the level of capability that you get out of such a system.

What is your geographic location...? Depending on where you live, someone might be able to point you towards someone that can help.

Cheers

 

[IronFish]

HPost,

Thanks. Sometimes all you need is someone to tell you what the right language so you know what to ask for. "Proportional pressure reducing valve" sounds good to me. The automation can wait until I get paid for this first job. Thank you.

Jeff

 

[hydtools]

Perhaps fit the system with a pump screw like that found on a dead weight tester. Turning the screw out will controllably and accurately reduce pressure.

Ted

 

[hydroman247]

Am I missing something obvious? Can you not just run a simple circuit with a relief valve that you wind in and out?

 

[HPost]

Yes you could that, but it will generate heat unnecessarily. It will require a constant pressure source such as an accumulator, but it will be far more efficient.