Spool valve help please.

[etpm]

Today I took apart the spool valve on the power steering cylinder I bought for my Yanmar YM2310. It needs, in my opinion, a piece welded into the slot in the end of the spool to make it stronger. When I took it apart the o-ring on the spool was damaged and there was rubber debris in the valve body and the spool grooves. So it's a good thing I took the spool out. The valve and cylinder are new and have never been used. I felt inside the valve body and could not find any sharp edges that would tear an o-ring so I'm thinking that the oil used for assembly was just too thin and let the o-ring catch and tear. I would like to use some sort of assembly lube or grease when I put the spool back in. I can't imagine that a tiny amount of grease or 90 weight oil or something similar would cause any problems but I don't know. Anybody here know?

Also, even though I have made plenty of spools and valve bodies in my long career as a machinist I have only assembled a few. The lands on the spools always have sharp edges after being ground and these edges were never broken on the spools we made. Every spool I have ever seen is made this way, and the spool in the valve I took apart today is no different. Anyway, the sharp edges makes assembly a little fussy because the sharp edges of the spools could catch in the bores of the valve bodies when the spool is first being inserted. This could of course damage the valve body and cause, or could cause, leakage. So, I figure the edges of the lands on the spools are left sharp for some reason besides saving a little money by not taking time to break the edges. Is that right? The edges need to be sharp? Maybe this makes the metering work better?
Thanks,
Eric

 

[oldnslo]

I will try and answer some of your questions

yes the spool edges should be sharp. This is to help reduce leakage from reduced overlap and also reduces flow forces which is more of a concern on solenoid operated valves. Yes you have to carefully work the the spool in never use force. A little will hurt nothing during assembly other than make your fingers slippery so you drop more stuff… well at least I do

Are the scratches on the spool from debris trapped between the bore and spool or intentional metering slots? If steering I would suspect some form of metering slots on the edge of the lands.

On the O-ring possibly - probably nicked during assembly process. No disrespect to anyones assembly skills but it can be very easy to nick an o-ring on those sharp spool edges. Does this O-ring fit in a counterbore of does it just slip over end of spool and held in place by a cover? If in counterbore you have to study the spool and figure how to have spool installed in the body and still be able to install the O-ring since there is no way to slide the spool lands through the O-ring with out damage to that seal.

hope some of this information is helpful

 

[etpm]

I will try and answer some of your questions

yes the spool edges should be sharp. This is to help reduce leakage from reduced overlap and also reduces flow forces which is more of a concern on solenoid operated valves. Yes you have to carefully work the the spool in never use force. A little will hurt nothing during assembly other than make your fingers slippery so you drop more stuff… well at least I do

Are the scratches on the spool from debris trapped between the bore and spool or intentional metering slots? If steering I would suspect some form of metering slots on the edge of the lands.

On the O-ring possibly - probably nicked during assembly process. No disrespect to anyones assembly skills but it can be very easy to nick an o-ring on those sharp spool edges. Does this O-ring fit in a counterbore of does it just slip over end of spool and held in place by a cover? If in counterbore you have to study the spool and figure how to have spool installed in the body and still be able to install the O-ring since there is no way to slide the spool lands through the O-ring with out damage to that seal.

hope some of this information is helpful

The spool has several lands, the o-ring, then some washers and a spring. So the o-ring is the last thing to fit into a bore and then seal. The spool was obviously shoved into the bore with little care. I will not duplicate this lack of care.
Eric

 

[npalen]

I've found a very small amount of STP of use in this type of assembly. As for the o-rings, I don't see any particular difficulty in slipping them over each end of the spool after it is installed in the valve body. Just avoid sharp edges that might damage the o-ring.