How much pressure? How long stroke? Why steel? Why .696"? Blow out the
bore to .75" would allow you to use off-shelf parts.

I may not be able to give definitive answers to your questions, Tom...
but here's a quick and dirty on what I'm up to.
Picture a track mounted backhoe (small size called a mini-excavator).
This unit has a dozer blade for pushing the dirt back into the trench
upon completion of the job. The dozer blade leaks off after raising it
up with the control. I checked the cylinder and with the blade raised,
and both the cylinder ports plugged, the blade stays in the raised
position. I thought it was the valve, but upon further inspection, no
problem in the valve either. This unit is made in Japan, sold in
England, and there is not much info in this country (USA) concerning
it, however I had been e-mailing some guy in England and was informed
that my problem was more than likely the "rotary coupling" used in the
center of the machine to couple the upper framework (which can rotate
360 continuously) to the lower framework (which consists of the
tracks/motors and the dozer blade/cylinder). This prevents hydraulic
hoses from winding around in the machine. I understand the rotary
coupling will permit fluid to circulate and the blade to drop.
Replacing this coupling would be a monumental task, totally out of my
realm of possibility (and extremely expensive), so I decided to come
up with a different idea.
The only kind of a check valve I can seem to locate is a piloted
check, which I don't want to use. So I am making a block of aluminum,
with 1/4" pipe connections for input and output. From EACH of the 1/4
pipe fittings, there will be a channel going to the center of the
block and appearing at the bottom of a flat bottomed hole. A piston,
with a stout spring will push down on the flat bottom of the hole and
"seal off" the two channels going to the 1/4" ports. The amount of
pressure needed is only a few pounds to prevent the oil from
circulating around and letting the blade drop. As the operator lever
is moved, hydraulic pressure from the pump will overcome the little
piston (doesn't matter which DIRECTION of flow) and the blade will
raise or lower as needed. When the lever is released, my little
piston will seal off the two holes again, holding the blade in
position. That's it. I came up with the size as my "channels" are
7/32" holes, spaced 1/8" apart from each other in the center of the
piston bore, with a little bit around the outside. It can be any size
I need, but the smaller the bore, the less pressure I will need to
seal the ports.
Am I crazy? or will this work.....
Ken.