YW-6 Backhoe Problem

[TruChaos]

Well I finally got around to working on the control spool assembly. I decided to "do it right" and remove the entire valve assembly, put in the parts washer clean everything thoroughly then disassemble the relief valve assembly and flush everything out with clean solvent. I figured I'd flush all the spools and reinstall the assembly.

Well, in classic Homer Simpson form, I cleaned off the valve assembly then proceeded to remove the relief valve components. I placed my hand on the relief valve cap and it was on the last couple threads.

The relief valve adjuster had worked it's way completely loose and wasn't making contact with the bottom of the relief valve plunger. I haven't reinstalled the spool assembly but I'm sure that was the problem.

DOH!

 

[RonMar]

I always like it better when I find SOMETHING wrong Now you will need a pressure gauge on the system to set the relief valve properly...

 

[TruChaos]

Well technically I suppose there was a problem. When I took the relief valve apart, I really had to pull to get the top spacer and O-ring out. The O-ring was broken and I'm not sure if I broke it pulling on the spacer or if it was already broken. I replaced it with a Fluoroelastimer chemical resistant O-ring.

Any advice on finding a metric adapter with a 1/4 NPT side port for the pressure gauge?

 

[Smalljobs]

I made up a spacer and attached the gage in the middle. You could sandwich something like this between the normal Chinese hose connector and the pump. The location is not convenient but it's only temporary. Send me an email and I'll send you more detailed photos.

Ronald at Ranch Hand sells an adaptor like this and I believe it's used to convert to JIC, like my home made one.

The tapped NPT outlet on mine is roughly the size of the Chinese flow passage and this allows me to either thread in an NPT or else just sandwich it in between the pump and flanged Chinese adaptor.

 

[RonMar]

The output ports on your control valve should be a straight 18MM metric thread. Into that threaded port is screwed an adapter that gets from that metric port to the O-ring face seal hose fittings used by the hoses. You should be able to buy a straight metric to female NPT adapter. I think it is 18MM X 1.5MM thread pitch, but you can take one of your hose adapters along to match threads. When you get the adater and gauge, you can just screw it into one of your working ports in place of a hose adapter and then send pressure to that port. Put the disconnected hose in a bucket incase you send fluid the wrong way and of course make sure the BH is properly supported before disconnecting ANY working hose...

I found the adapters thru my local hydraulic supply shop for about $8... Not specifically familliar with your valve but on my HW-03 BH, it has a single input checkball located directly above the pressure relief valve. You access the ball and spring by unscrewing a large straight slotted screw plug on top of the valve body directly above the relief vlave. If you have this plug, the metric adapter I mentioned above can be modified slightly to screw in place of the plug(same metric thread pitch), and system pressure can be measured at that point also. If you PM me an E-mail address, I can send you a diagram on how to modify the adapter to fit in place of that screw plug. I made a few of these for people a few years back, so there is a thread here with the particulars and some pice of the gauge installed on my BH...

 

[TruChaos]

Thanks for all the info Ron.

By the way, you mentioned a check ball under that screw and spring. I took mine out and there's only a spring. I can look down and see the top of the pressure relief plunger. Which is flat with a small detent in the top.

What is the check ball doing?

 

[RonMar]

The checkball is there to prevent fluid from flowing back thru the pump if the load on the hydraulics should generate a higher pressure than the pump is outputting... If only one control is moved at a time, it prevents uncommanded movements. IE, I pulled the lever for up, and the boom went down. With the checkball in place, this should never happen, and up should equal up, or no movement if the pump cannot overcome the pressure in the cylinder. On this hoe, if you move more than one control at a time, you will get uncommanded movements, like if you do boom up and bucket curl at the same time, the boom will actually go down and the bucket will curl faster as the heavilly loaded boom feeds pressure backwards thru it's valve to feed the lightly loaded bucket. More sophisticated valves have a load check on every spool valve, so this dosn't happen. This valve has only one...

In the attached drawing of my HW-03 valve, the fluid from the pump comes in from the left. With no controls active, it flows straight down the middle to the return line and back to the tank. When you activate a spool, the center path is blocked so the fluid flows up past the ball (circle in v) and to the commanded spool and out to a cylinder. The fluid comming back from the cylinder passes thru the spool and out the return line along the bottom of the diagram. IF the cylinder being fed fluid stops moving, flow stops, pressure builds, relief valve(below checkball) opens and fluid is dumped into the return gallery which ties to the return port and hose back to reservoir. I am guessing your valve is pretty similar, and having a spring in the hole tells me that it should probably have a ball also, as without the ball, there is no need for the spring...

 

[TruChaos]

Interesting. I certainly agree about the spring, it's not doing anything without a ball. The ball certainly wasn't lost when I took it apart. I slowly removed the relief valve on a plastic cart with 4 inch high sides all around and no parts were lost.

Maybe the ball fell out of position and is lodged in the port somehow? How big is the check ball? Is there also supposed to be a washer or some type of capture between the ball and spring? If so, that's not there either.

I'm almost tempted to buy a replacement control but I don't want to go through the added expense and frustration of fining inch to metric adapters for the hoses. While the replacement control is expensive enough the adapter costs add up fast. I learned this when I replaced the loader control.

Thanks

 

[Bob Rooks]

Not all check valves use a ball. Some will have a ported cylindrical slug that the spring nests inside.

 

[TruChaos]

Not all check valves use a ball. Some will have a ported cylindrical slug that the spring nests inside.

Well, I took it back apart and didn't see any check balls. I removed the relief valve assembly and the screw from the top. I didn't see a slug that comes in contact with the top spring and I tilted the control hoping a check ball would pop out. It didn't. I carefully probed the screw opening (where you said a check ball might be) and the bottom of the hole felt like it was slightly concave with a hole in the center. I put it all back together and ran it with the relief valve adjuster only turned in a couple turns. It works fine and now has the power to lift the boom and lift the rear of the tractor with the outriggers.

The good news is that it works, didn't explode and has no leaks. However, the original problem of the boom sagging after time still exists. I can live with the sagging as long as everything functions.

Thanks to everyone for all the help and advice.