I have two of those long-stem Worcester valves that I use on the test
stand as manual fill valves. Very nice valves and they turn nice and
smooth when cold. But they are very heavy. I recall the stem seal
being a bunch of PTFE washers compressed together or something similar.
With enough compression, the washers cold flow and make a seal.
I also have two cryo MCF valves on my test stand connected up to rotary
air actuators. They are quite hard to turn when cold and in particular,
the one I'm using for the LOX vent valve on the stand is very hard to
turn because I mounted it with the stem facing down. It doesn't leak
but you have to either use a heat gun on it or loosen the body bolts to
get it turn when cold, even at 120 psi with fairly large actuator. For
the next static test I'll reorient it back upright.
-Bob
On 05/30/2016 11:19 AM, Henry Vanderbilt wrote:
I believe Worcester offers short-stem options for cryo valves. The drawings at https://www.flowserve.com/files/Files/Literature/ProductLiterature/FlowControl/WorcesterControls/WCENBR1040-01.pdf may tell you a bit about how they go about sealing things.
Henry
On 5/30/2016 8:52 AM, Robert Watzlavick wrote:
What kind of stem seal did they use? Was it the type where you have a
cone that squeezes into a sleeve?
I hadn't seen any short stem cryo models. It might be worth me getting
one to take it apart. Were these custom or off the shelf?
-Bob
On May 30, 2016, at 10:24, Ben Brockert <wikkit@xxxxxxxxx
<mailto:wikkit@xxxxxxxxx>> wrote:
To be clear, basically every vehicle I've worked on had short stem
cryo ball valves, and most of them did not leak. Torque requirements
are another issue, but it is not a universal truth that all short stem
ball valves leak out the stem.