spool valve

[IHJIM]

Hello Again!
I am working on a Massey Ferguson 50c backhoe loader. The backhoe boom has very little downward pressure, it will press down a little bit but it won't come close to lifting the rear of the tractor off of the ground. It picks up just fine w/plenty of power. Also, if I set it on the ground and let go of the lever, I can extend the extenda-hoe out and it will push the whole boom up...so the spool valve must be letting the fluid past and allowing the main cylinder to relieve pressure when it is not supposed to.

I am about to tear down the spool valve and was wondering what to look for once inside of it.

Thanks,
Jim

 

[willie59]

Sounds like it might be failure of a circuit relief valve on the boom down side. But I have no clue what kind of valve a Massey 50 used, not much help there.

 

[IHJIM]

Is the circuit relief valve located in the spool valve's block?
Sorry if this is a dumb question.
Jim

 

[willie59]

Typically they are, and are servicable without complete valve disassembly. But again, I know nothing about what valve your machine has.

 

[oldseabee]

Before you tear the valve apart, what pressure are you seeing when trying to push down with the boom? Each circuit has a circuit relief in each direction, and some of them have different pressure settings, generally set higher then the main relief. Most likely that is where the problem is not the valve itself. There is slight possibility of an intenal crack in the valve.
get a pressure reading on the boom down circuit and compare it with the other circuits. If it is way low, see if it is adjustable some are and some are preset. If it is adjustable, loosen the jam nut and back the screw out several turns, be sure to count the turns so you can reset it, then try the boom down. sometimes a piece of trash can get caught under the poppet and bypass. By loosening the adjustment, the trash may get blown on through. The other possibility is a loose piston in the boom cylinder, when you retract the cylinder, the piston can come away from the rod and bypass internally. when you extend the cylinder the piston is pushed back on the rod and seals up so you have pressure there

 

[oldseabee]

The circuit reliefs usually are located next to the spools, two per spool. Find the hose that pulses or tightens up when you hit the boom down lever, the circuit relief should be located near where that hose connects to the valve.

 

[IHJIM]

There are 5 valves on the spool block section that is causing the problem. 3 of them are just a threaded end cap with a spring that holds a plunger against a seat, they are located on the back of the block. The other two are located on the top and bottom of the valve block. They don't look like they come apart, they have a strong looking spring inside. Is there any way to tell witch one is causing the problem? By the way, there are 7 spool block sections that control the backhoe. I know witch one controls the cylinder that is acting up.

I am a 17yr old so I don't know all of the correct terms to use for this stuff, and I have never wrenched on a spool valve assembly before so bear with me.

 

[willie59]

Would it be possible for you to post a picture of the control valve? That would help a lot.

 

[IHJIM]

Here are some pics of the valve block. The section that is causing the problem is the one with three slotted plugs on the back.

 

[IHJIM]

More pics.

 

[willie59]

Well, a few things to noodle through here. Pics are good.

First, those hex head cartrige things on the ends of the 4 valve sections are circuit relief valves. Pressure value is pre-set, not adjustable. The relief valves that are in the boom up/dwn section, clean the hex head real good and see if they have some numbers stamped on them. If the numbers are the same for those two cartridges, I'd switch them and see if you now have a problem lifting the boom, which would indicate cartridge failure. Even if the numbers are not the same, I'd still be tempted to switch them.

Second, replace all the seals now that you have the valve body removed. I'm not sure what size the seals are for the spools. As for the fittings, all those hose fittings are SAE o-ring boss, they take a 900 series o-ring; like 568-901, 568-902, 568-903, and so on. The cartridge valves use 900 series to seal the hex of the cartridge, but the o-ring at the tip of the cartridge valves is most likely a 100 series o-ring; like 568-111, 568-116, 568-118. I would replace those teflon back up rings on the cartridge valves as well. And personally, I'm not fond of those split telflon back up rings, I prefer the moulded back up rings, no split in it.

Third, those thingys under those flat head caps, those are poppets. The large one would come from the port in the center of the valve section, those are the internal power beyond poppets. The small poppets that came out of the boom up/dwn section, I'm not sure what there function is without inspecting the valve workings, but I don't think these poppets are causing your problem, can't say that for certain though. Also, the o-ring on those caps are 900 series.

A few random thoughts, you did make certain to not mix up which section each spool came from, as most of the time those spools have different machine work about them. And what kind of no brain never have to work on it design engineer makes hoses thread directly into a valve body and not use a swivel fitting on the end, then other hoses/fittings on the same valve have JIC #8, #10, and #12 female swivel fittings??? A hose with no swivel is a bi-itch to remove from the valve body when ya blow one, good grief!

 

[IHJIM]

Thanks for the reply!
Yea, I was originally planning on taking the whole thing off of the tractor to work on it, but those non swivel hoses put a veto on that idea. Every seal that I have encountered so far is some form of O ring. Will the O rings that Napa sells do the trick? Even the spools were sealed with O rings. Where do you get the split teflon backup rings, or their equivelant, at?

The poppets "looked" like they were sealing-there was an un tarnished rim around the face of them where they sealed on the block.
If one of the hex cartridge relief valves were bad, can they be rebuilt or do you have to find a replacement? Are they still even available?

Luckily, I kept the spools in order. Sorry for all the questions...I lack the experience that you all have.

Thanks again,
Jim

 

[willie59]

When cartridge valves go bad, they are typically FUBAR. Good question if they are still available, I wouldn't know about that. But if they are, probably not cheap.

I don't know if NAPA is going to have 568-100 series o-rings, they might, just don't know. Same with the 568-900 o-rings. All I can tell you, if you use anything other than 900 series o-ring boss o-rings on those straight thread fittings, the o-ring will fail. I don't know how you are with funds, but if you're going to have that machine for a few years, I'd purchase some o-ring kits. Check out this link, the second kit pictured (U.S. Industrial o-rings) has most of the 100 series o-rings you'll need, plus 200 series you'll find on your machine as well. Scroll on down to the Boss Seal o-ring kit, you need that one, Buna-N 90 durometer. The back up rings, that's a little tricky. If I knew what size 100 series o-ring was on those cartridge valves, I might be able to find them online for ya, but I'd have to know what the proper o-ring is.


http://www.oringsusa.com/html/o-ring_kits.html

 

[oldseabee]

See if there is a brand name on the valve assy, it looks like a Commercial Brand, but anyway if you can find a name and maybe a model number go online to the manufacturer of the valve and see if there is a tech help line to call up. They may be able to help with the reliefs and O rings and maybe a parts breakdown.

 

[capnkel]

Im not so sure thats a Commercial Shearing valve.My Case 530 has a C/S V20 series valve,it looks nothing like that one.Of all the valves i've run across it might possibly be a Cessna valve.
As for seals,i'd look on the internet,and local phone book,most larger citys will have a company that specializes in seals of all types,best thing is to take the parts needing orings,they will measure for proper sizes there,as most orings on that valve have been distorted from being used making exact sizes a bit harder to judge.If you get new spool seals,id ask for quad rings in the same size as the orings,they seem to hold up better.
Those hoses with the solid hose ends SUCK,looks like ones ready for replacement anyways,very easy to add an oring to jic adapter in the valve,and get a hose made with the jic swivel,much,much ,easier to work on.Good luck.

 

[oldseabee]

The point that I was making was to see if he can find a brand name and model number on the valve and go online to the manufacturer of the valve if they are still in business, and call the tech service dept. for info on that valve.

 

[IHJIM]

I just found that it is a Cessna spool valve.