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System not maintaining pressure

System not maintaining pressure

System not maintaining pressure

Hi all,

New to the Forum(any forum really) and fairly new to hydraulics but I have an issue I cannot seem to fix. Hopefully someone on here that know a lot more than me can chime in with something I haven't thought of.

I have a pretty simple hydraulic system on a large roll calender (or roll mill) here at work. The machine is used to compress battery electrodes to a desired thickness/density and recently has been unable to compress the electrodes to an acceptable level. A local repair company came out multiple times and after replacing a few valves, and costing a lot of money, the system was still not fixed. We decided after that to just do the work ourselves and replaced all the other valves and the pump itself. The system worked quite well after that for a month or so until someone decided to increase the system pressure and things have all gone wrong again (it has since been reduced to normal and did not exceed the 5000 psi rating of the valves and fittings). I am pretty new to working on hydraulics more complicated than a simple braking system on a car or motorcycle but I understand well the theory of fluid power. I will describe the system the best I can with my limited knowledge of the proper terminology.

The pump goes into a check valve, and then into a stack of 3 manifold blocks. The first and closest to the pump is an RDDA valve, a relief valve. Next is the PRDR, direct acting, pressure reducing. After that it goes into a directional valve and onto the cylinders. The cylinders are what raise the lower roller to a defined gap between it and the upper roller. They are dual acting and there are 2 of them. There is also a nitrogen accumulator.

Now that you have some backstory and the system description, here are the problems. As mentioned above, it no longer can achieve the density desired and also cannot maintain pressure after running for a short time. The system cycles up to 3200 psi and shuts down until the pressure drops below 3000 psi and cycles again. After running for a short time (<15min) the system can no longer maintain pressure and the pump runs continuously with the pressure stalling out around 3000 psi. I have been trying to bleed air out of the system and have got a fair amount out but it does not seem to be making a significant difference and does make sense to me that air in the system could keep it from maintaining pressure after a short time when it was working fine previously. Any ideas or even corrections of some improper terminology are appreciated as I am trying to learn all I can quickly.

https://files.engineering.com/getfile.aspx?folder=... - Cylinder 1
https://files.engineering.com/getfile.aspx?folder=... - Roll calender
https://files.engineering.com/getfile.aspx?folder=... - Power unit

RE: System not maintaining pressure

Have you got a schematic diagram for the circuit. If you have, it would be worth posting a copy (recommend using the image button rather than posting links to files in the cloud - people are understandably cautious about downloading files off the net).

If you haven't got a schematic, it would be a very useful first step to try to draw one (based on datasheets for the components and your best understanding of how they go together). As well as giving people here something to work with, the act of putting the schematic together will help you understand your system and may well lead you to work out the solution for yourself.


RE: System not maintaining pressure

Make sure your relief valve is set higher than your pressure reducing valve, oil running through the relief will generate heat quickly. Also check the accumulator pre-charge.



RE: System not maintaining pressure

#1, your reservoir is very small and may contribute to a high operating temperature which will result in short seal life.

#2, your system appears to have an accumulator. Without a proper gas charge this will cause short cycling.

RE: System not maintaining pressure

If the pump is running continuously at 3000 psi and still moving any quantity of fluid, it will be generating heat somewhere, wherever the fluid goes from 3000 psi to atmospheric pressure before returning to the tank. Finding where that heat is generated will tell you something (if you have an IR camera they're great for this, but a bit overkill for this system). I'll second zeusfaber's suggestion to get the schematic (and posting it here). Trying to troubleshoot a hydraulic system without a schematic is pretty useless, at least I find it to be.

It would also be a good idea to take a look at the controls side of this system to make sure you don't have an problems there and to understand what is supposed to be happening.

RE: System not maintaining pressure

You have 4 links to images.
If you use the "Camera/Image"-button those images will show on the screen and you will have a much better chance to engage someone with a good answer for you.
The attachment feature is meant for text documents

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