New here, working on a 275B loader with no loader functions, every port I have tested on the main pump and at the control valve tests "0" with 2 different gauges, removed and resealed main control valve, only really found a worn o-ring and backup ring on the pilot relief, didn't feel that was enough, remove relief valve from main pump, found o-rings completely missing, removed pump and resealed, several pocket seals were torn and missing, reinstalled pump and refilled tank, pressure is still 0. Today I backed the pump out of the converter just far enough to verify that the pump is in fact being turned by the converter. The transmission works (different pump), steering the machine will wiggle it and on the back of the steering pump is another pump which ties in with the main hydraulic pump. I can't fathom that even a missing o-ring or a broken relief spring somewhere would show absolutely 0, but I can't build any pressure almost like the pump isn't even turning. The operators say they shut it down working and when restarted had no functions, although they have admitted that it didn't work well. Any ideas would be greatly appreciated. JW
im not really sure on the 275b but 120b has a pilot pump on right side and follow lines and see where they go (should be a valve body with line going from it to brakes and steering with a servo ..look and see where hoses go from steering back to pump thier should be a servo valve and 2 adjustments (dont mix them up both have different pressures) and a magnet servo unscrew each one at a time and shove a rag in hole cause fluid is going to pour out now i used a vise and pipe wrench and unscrewed the end off (becareful dont mess it up with pipe wrench )and their was pieces of packing in Now at the bottom of steering there should be a valve with 4 hoses P= pressure T= tank and l=left r=right take the p and t line a loose they have a small spool with a spring its like a directional valve ive seen them break on p side and you had steering then nothing but jerking spool had turn sideways and engine off no pressure is would turn sideways after a lil pressure it closed port off
Ok i forgot jeff doing test on volvos are different ....on the front diff there is a control unit look at the lines one tilt in tilt out lift up( try to firgure out which is which by tracing lines back from pressure fitting heres the thing i see and a friend here tolded me hook up tilt fitting raise lift 3 feet off ground at idle and tilt bucket in til it stops and hole it 5 secs thats working pressure my L120b should be 3650+ or - 80 then change pressure fitting to tilt out and raise bucket 3 feet and tilt all the way out L120b pressure is 1150 +or_80 they only read working pressure
Thanks for the reply, I downloaded a parts book off Minnpar, and was looking for a suction screen in the bottom of the hydraulic tank, I'm thinking I can't get enough oil to the pumps, I have checked my oil pressure at the pilot valve in the cab and have absolutely "0", won't even wiggle the needle, checking at the main hyd. pump shows 0 pressure as well. If there is any oil flowing I would think I could build a little pressure.
Just to be clear, do you have good steering pressure? Then the problem is in the bucket/boom system. That system uses a pilot operated Husco split spool valve located in the front frame. The inlet section contains a main relief valve and a flow control valve. The flow control valve sends oil back to the tank when the system is not being used. If it is stuck open then you won't get any functions to work. If the main relief is stuck or broken, same result. Still, if you have flow there should be some back pressure. The pump is a two stage pump that gives both stages at low pressure for speedy lift and drops out the front section at high pressure to prevent loading the engine down. If you have absolutly no pressure then the pump is broken or you are not getting any oil to it. Check for collpased suction line, there have been cases where the lining comes loose but the hose looks OK from the outside. The steering and hydraulics get oil from the same tank, the transmission charge pump gets it's oil from the transmission sump.
oldseabee, thanks for the response, I have already removed and resealed the main control valve and just couldn't find enough issues in it to make me think it was a problem, so I kept hunting and thats when I found the seals blown off the relief in the center of the main pump, I removed that pump and resealed it, some of the pocket seals were missing and that section of the pump had those installed on the inlet side, after a few phone calls I reassembled the pump with all of the pocket seals on the discharge side. When I run the machine I still have zero pressure at the main control valve and at the pump. I agree with you if I had any flow at all you would think I would see at least 10 psi or so back pressure. Something is bothering me, when I removed the main pump the oil drained down in the "y" pipe just enough to remain at the bottom of the pump, and that is with the main hydraulic tank empty and the plug removed from the bottom of the tank, I'm not sure how the tank is built internally but it appears that the oil in that pipe should have freely flowed out the bottom of the tank, also when I remove plugs from the main pump I am getting air out and even after bleeding I still get no pressure. I am going back tomorrow to first check my steering pressure and then drain the tank and remove the "y" pipe, if my steering pressure is low I am thinking that I can't get enough oil to the pumps. thanks jw
jeff open top on hydralic tank see if pressure is built up and remeber dont get oil bath no oil bath you got blockage or bad pilot pump
To get at the suction screen remove the filler cap and the plate that it screws into. then reach down to grasp a "U" shaped handle and unscrew it the screen is attached to it. The suction gets it's oil from the upper part of the tank to keep it away from any sediment in the bottom. If the screen gets plugged there is a bypass valve set at about 2.5 PSI that should prevent starving the pumps. The level of the screen just a little below the level of the pump inlet so that is why the supply hose holds oil instead of draining out of site. The other solid round plate on top of the tank is where the return filters are.
Well I'm running out of answers fast, checked steering pressure at the pump - 2200 psi, removed top of tank and looked at suction screens, both look clean with no sediment, oil level gauge is missing but oil is above the top of the suction screens by about 4". Still absolutely 0 pressure measured at the main line going into the loader control valve. I have proved that my bottom 2 section hydraulic pump is turning, the top pump attached to the steering pump I am assuming is turning because I have steering pressure. Will that Husco valve flow enough oil through it and back to tank to build up 0 back pressure? I don't own a flowmeter yet but I wish I had one to put inline so I could prove this out. Hate to go buy 2 new pumps if the issue is really in the control valve. Customer is being patient sounds like I'm the third guy they've had working on it. JW
When you see "0" pressure, is it with a high pressure guage 3000 PSI? You may have some low back pressure but not enough to register. Try a low pressure guage that will be more apt to pick up a very low pressure. The flow control in the main valve doesn't offer much restriction back to the tank, but there should be some from the return filters. There was 2 style pumps on the 275B, the early ones had the control mounted on top of the pump, the later version had the control built into the center between the sections. The old style had the high pressure section at the rear of the pump and would unload the front section back to tank. There were cases where the shaft between the two sections would break, this would cause the gears in the front section to loose support and eat up the case so it couldn't create enough suction to prime itself.. The new style pump had the high pressure section in the front of the pump. If you run the machine for a while to build up pressure in the tank, then shut the machine down, lossen the outlet fitting and see how much oil the pump will bypass, if the pump is good you should only get a trickle of oil but if it is bad you will get quite a bit of oil.
Thought I would post some results, I ended up removing the flow control and the main relief valve, disassembled the relief, cleaned it up and really didn't find anything in it like I thought I would. Put it back together, fired it up and it went to working, I can tell the pumps are weak, but the customer says it is working the best it has since they've owned it, appreciate all your help, Thanks JW