OT, Hydraulic Issue

Okay folks, I know this is OT, but there is a PLC involved. I am looking for suggestions on this system I am working on. Peter N, I would be interested in hearing what you have to say.

This is a HPU with a 100hp motor and a 20hp motor, both motors are running Linde Load Sense Piston pumps. The pumps are currently feeding oil to solenoid valves, the valves are then feeding intensifiers. What I am seeing is the pressure graph attached. I am worried that this rapid spiking and dropping of pressure will wear out the pump controls in short order.

The intensifiers are mechanically switched, when the piston gets to the end of stroke it shifts a small pilot valve on the intensifier and directs the flow to the other side of the piston and it changes direction and moves the other way.

I have access to several Servo-Proportional Valves with P/Q functions that I can use if I have to.

Now would there be a way to somehow predict when the intensifiers are going to shift and control pressure accordingly or am I just barking up the wrong tree here.

Any suggestions would be helpful.

Thanks,

Edm

Do you have accumulators after the pumps and before the valves?

Keith

Its pretty hard to help without a circuit but that is pretty much what intensifiers look like on a pressure plot. They are basically little single piston pumps so when they are retracting, the pressure is low and when they are extending the pressure is high. They kind of sound like bad lifters in a car engine but you have to be old enough to know what that means ;-)

Accumulators could help as Keith said but you may have to put in some additional circuitry to make sure you can still get to full pressure when you need it.

Not sure what the proportional valves will be doing for you....?

An accumulator will help.
Then the flow out of the accumulator will need to be controlled.
What is the application?

Yes, I think an accumulator would be good for the system, the proportional valves will be used to vary the flow to the intensifiers, but I dont know if they will help with the spiking.
Application is a pressure testing system.

Thanks for your help guys.

Cheers.

More information is always helpful. It looks to me like the spikes are caused by the pump but a cycle is about 1 second. In this case the accumulator will reduce the spikes. If you are using a single piston pump like Norm suggested it is easy to calculate how much the pressure will spike at the output of the pump with different accumulator sizes and pump displacements. The volume of oil that needs to be pressurized must be small relative to the pump displacement to get such big pressure spikes. The valve will just let oil in or out to control the pressure but control is easier if the pressure supply is relatively constant.

accumulator and an controllable pressureoverflow is needed.

Thanks guys, I have told the customer to use a couple of accumulators on the system, they have some 2.5 gpm accumulators laying around. I will get them to precharge them and check the bladders then they can put them in. Since my data acquisition is not very fast, I can pretty much guess that there are a lot higher transient spikes going on than what we are seeing. Hopefully the accumulators will help.

My thought with the servo proportional valves is that I can flow control the output to split flow between intensifiers when they want to do multiple tests. And since they are P/Q valves perhaps I can set them up to limit max pressure in the system. Dont know if it will work, but I have the opportunity to try.

Thanks for the suggestions.

Edm

Are you sure the 2.5 GPM accumulators are big enough? Do you know what to pressure to pre-charge them to?
http://hydraulicspneumatics.com/200/TechZone/Accumulators/Article/False/43954/TechZone-Accumulators.

The precharge will vary depending on what the max pressure they need out of the intensifier. It's been a while Peter but I still remember how to calculate for an adabiatic accumulator sizing. Just guessing from other applications where I have used accumulators for shock absorption but I think 2.5 gals will do. Luckily the customer uses nitrogen in other areas so they have bottles and a charging kit already.