Jump to content

Need some hydraulic help please


Recommended Posts

You may have seen my post about my trials with re-plumbing my press. Well, I have a new/old issue. I have been making damascus billets this week, and running the press fairly hard. Today as I was squaring a billet the filter case ruptured. This is the 3rd time. The filter is on the return line and is made for hydraulics. I was going along just fine and the the case split open, which sprayed the forge case with hydraulic fluid, which promptly caught fire. There were several bwown twouser moments, including when, in an attempt to stem the flow of oil I closed a valve on the return line (without first shutting down the pump) which caused a piece of black iron pipe to part ways with the shutoff valve. Note to self, all valves are to remain OPEN unless the motor is first shut off.

 

Question 1) Just what is the pressure in the return line? I have looked at hydraulic filters in a couple of places, and they mostly say 100 psi limit.

 

Question 2) Can I run without a filter for now? I'd like to finish my billets.

Link to post
Share on other sites

Question 1) Just what is the pressure in the return line? I have looked at hydraulic filters in a couple of places, and they mostly say 100 psi limit.

 

No clue it would depend on your pump and ram setup. I'm not a hydraulic guy but I know I've had to buy high pressure filters before for farm equipment. Check grainger they aren't cheap though and you need to consider how much flow you need as well as the max pressure rating.

 

 

Question 2) Can I run without a filter for now? I'd like to finish my billets.

 

I've seen pumps destroyed from dirt and junk. That said you might get away with it. Personally I'd play it safe and wait.

Edited by Chris Vanco
Link to post
Share on other sites

Hi Geoff

 

something is wrong.. in your typical system with a return line filter... you should have a bypass valve set at a given pressure.. if the pressure spikes up and your in danger of exceeding your filter's pressure limit, the bypass valve should kick in and dump the excess to tank (averting the filter from rupture )

 

as to why you have high pressure ?? could be the filter element is too small to handle the max flow ?

 

perhaps go to a larger filter

 

- check the bypass valve to see if its jammed shutt

 

 

 

Greg

 

 

Chris has good advice not to run without the filter.. could be expensive

Edited by Greg Thomas Obach
Link to post
Share on other sites

I had the same problem.. I would wager that our filters are just too darn small.

 

terrifying isn't it? and a terrible mess, I've only just gotten my area cleaned up..

 

lots of sawdust and cat litter..

Link to post
Share on other sites

Well if I can get the control box for my hammer wired in you can come by and use my hammer if ya want.....just bring yerself a chair to sit on...

Edited by WmHorus
Link to post
Share on other sites

I blew up the filter housing on my press once by shutting off the motor and 5 minutes later walked by and closed the shut off between the return line and tank. About a minute later the whole thing exploded. The aluminum housing was rated to 75psi but everything was off. I realized that the cylinder still had 2000 psi on one side of the ram after shutting off the pump if I did not cycle the controll valve. When I closed the return line shut off the pressure bled into the return line and blew.

 

Now I shut off the press and cycle valve before closing the shut offs on both sides of the tank. I put those shut offs in to isolate the tamk in case of a laeak, My tank holds 20 gallons and I use a 9 inch tall 10 micron filter.

 

The return line should not have pressure on it unless restricted. My hoses and fitings are all 3/4 inch except the return line which is 1 inch. If you reduce the return line diameter any where including fittings it could develop back pressur.

 

Don't know if this helps

 

Matt

Link to post
Share on other sites

its not only straight pressure but the surge in the pressure........like water hammer in water plumbing.

 

there should be added volume in a tee fitting with a length of capped pipe to adsorb shock/surge. I will try to post a pic in the AM.

Edited by john marcus
Link to post
Share on other sites

Might be worthwhile adding a pressure gauge near the filter to see if the filter is getting plugged up. Not likely to be a line restriction there...To jump to something else, I found out the hard way that hydraulic oil is a powerful solvent that will dissolve some paints and coatings.

Brian

Link to post
Share on other sites

Geoff,

I agree with Matt... I'm some what different in that my feed line is 1/2" and the return line and all the fittings in that line are 1" including the filter..... I've never had a problem ....

 

and I would NOT run without a filter either... especialy if you are not sure that the filter is not getting contaminated and plugging up... I would think if the gaskets

 

in the the system were breaking down for some reason and enough material was in stream to plug the filter then I would think you would be having leaks and falling pressure....

 

I think John has a good idea with the tee and some fittings... a shock absorber of sorts...

 

Dick

Link to post
Share on other sites

The "water hammer" idea makes perfect sense, I'll do that when I rebuild the system.

 

My system is 15hp 3ph, 12gpm pump, 5 inch cylinder.

 

This filter is rated at 100 psi and 30gpm flow.

 

This one is rated at 200 psi and 70 gpm flow.

 

Then there is this bad boy. Overkill perhaps?

 

Does anyone have an opinion. I realize that I have to decide, but some guidance would be nice.

 

Geoff

Link to post
Share on other sites

The "water hammer" idea makes perfect sense, I'll do that when I rebuild the system.

 

My system is 15hp 3ph, 12gpm pump, 5 inch cylinder.

 

This filter is rated at 100 psi and 30gpm flow.

 

This one is rated at 200 psi and 70 gpm flow.

 

Then there is this bad boy. Overkill perhaps?

 

Does anyone have an opinion. I realize that I have to decide, but some guidance would be nice.

 

Geoff

 

 

the system in the picture is 20hp parts from surplus center

Link to post
Share on other sites

Geoff

 

I think any will work. The aluminum housings the filters screw into are usually rated at 100 psi or less. I blew the aluminum up not the filter. I agree the water hammer idea is good but preventing back pressure is required even with the hammer.

 

 

Matt

Link to post
Share on other sites

Geoff

 

i haven't posted or relied in a long time but work has been crazy busy and we got a dog from a rescue group and haven't been really reading or forging or anything, BUT this post caught my eye and I can help with this.

 

firstly the filter should not be on the return from the valve it should be in the pump suction line. the purpose of the filter is to protect the pump (and thereby the cylinder) from debris that is in the reservoir. the line going into the pump should also be larger than the actual pumps inlet size unless it is coupled directly on the reservoir.

 

if you are then still experiencing flow restrictions through the filter double them up in parallel, this will also reduce the pressure loss through the filters.

 

because the system is pressurized after the pump you can see full pressure and "water hammer" anywhere after the pump, so every component after the pump should be rated for full system pressure. i.e. don't place a 100psi rated filter anywhere after the pump discharge, suction side only.

 

please see the attached basic hydraulic circuit diagram (i hope it attached)the tank is on the right followed by the filter then into the pump.

then into a 3 way 5 port valve then into the cylinder. from the valve the "pan" is the symbol for open to atmosphere return, usually back into the tank behind a baffle to protect the pump inlet from any entrained air.

Hydraulic_circuit_schematic_directional_control.png

 

hope that helps, good luck

 

Joe

Link to post
Share on other sites

Thanks Joe, I was wondering just on a general level, why filter the fluid after it's gone through the pump.

 

Take care, Craig

Link to post
Share on other sites

Hi folks,

 

I stand corrected, at least from what I can gather. I peeked back at a handy manual on the subject, and sure enough it's recommended to hook up the filter on the return line. My thought was to remove grit before it got to the pump, but maybe not.

 

Take care, Craig

Link to post
Share on other sites

Craig

 

What manual?

 

All the Hydraulic system I've seen and design guides i have used have a filter before the pump at minimum. The cylinders(or motors)are closed and sealed and machine finished. The grit and debris come from the reservoir that is not finished and is open to the atmosphere (with air filter).

 

The Monarch hydraulic unit I bought to run my 40 ton press has a filter at the pump inlet and a strainer at each valve port. It uses soleniod valves and has some inline check valves, so those need to be protected from grit as well hence the strainers.

 

But as I tell young engineers as they come in, "ask yourself does it make senses?" you guys are bright think about where the debris is originating from, put a filter on every line if you like, but protect the pump. Plus if your blowing up filters that is not safe so it fails the question.

 

good luck and be safe, especially with hydraulics.

 

Joe

Link to post
Share on other sites

well, in my vickers industrial hydraulics manual it says that return line filters are reduced in effectiveness when exposed to shock, surges, pulsation, and vibration..

 

there is the option of doing it on the suction line, and pressure line

 

pressure filter is usually after the pump to protect the system if it grenades ( be a shame to toss a 40000 dollar transmission over a pump taking a poop ... you see it alot on heavy equipment )

- these look different ..its a change out element that goes into a thick filter vessel as its gotta handle system pressure... a real pain in the ass to change as there usually fine thread and almost alway on tight

 

suction line would be good aswell ...free from any surges.. just makes sure that there is enough flow to pump... starve the pump and you'll get some cavitation (little imploding bubbles that are bad bad )

Link to post
Share on other sites

Craig

 

What manual?

 

...."ask yourself does it make senses?" you guys are bright think about where the debris is originating from...if your blowing up filters that is not safe so it fails...good luck and be safe, especially with hydraulics....

 

 

I looked at the Batson manual from the ABS. I believe it only discusses 'return line' filters, and seems to feel that in that application, there might pump starvation due to filter restriction.

 

Good points, Craig

Link to post
Share on other sites

Craig - I'd want to protect the pump but...

 

Greg - Yeah Vickers is the reference but the complexity and safety issues on an excavator are a bit more than a single actuator and valve system. plus the expense of a high pressure filter more than frequently changing a low pressure suction side filter.

 

that would be more on an engineer vs engineer debate on the system design the given clients use, need and budget. I'm not one to baulk my system has strainers and filters on every port but that was from an articulated bus system so like and excavator and as Greg said you want to protect the system from a cascading failure.

 

Not sure if all this helps Geoff's original question but there is a lot of good info.

 

Now i can't wait to get forging again and turn on my press, i have two billets sitting since the fall.

 

PS Greg i saw Ontario and though you might be close but you are pretty far north, people think Buffalo is bad, got spring yet? :)

 

 

Joe

Link to post
Share on other sites

Hi Joe

i usta turn wrenches in the mines up here.. if it can be broken, miners will find a way ! it was mostly work on jumbo drills, scooptrams, and scissor trucks -- however the mines downsized and cut back alot on labour and i wasn't lucky, so i went back to university and moved on

- can be 6months of snow.. 3 weeks of spring, then the rest is mosquito season ( i'd happily live in buffalo rather than this place )

 

i believe theres enough good ideas on this thread to solve the problem.. hopefully

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...