[PSUBS-MAILIST] Swagelock needle valve

[Sean T. Stevenson]

Needle valves are designed as fine metering / flow control valves. While they can be used as shut off valves, maximum stem / seat life is obtained by incorporating an on / off valve upstream of the metering valve, and using this for shutoff so you don't ever have to torque down the needle valve to reliably cut flow to zero. Most automatically operated flow control valves fail open in their standard configurations for this reason, as it improves repeatability.

Also, be aware of the tightness of the packing nut around the valve stem, as leaks often occur here. If you want to get fancy, you can use a fine resolution / low range torque wrench on the stem, but for these small Swagelok valves it is usually sufficient to just feel the resistance to turning the knob.  You want enough compression on the packing to eliminate leaks and prevent vibration from possibly moving the valve out of position. Any more than that just increases wear on the packing and friction on the stem, making it more difficult to perform fine adjustments.

Sean



Private <alecsmyth at gmail.com> wrote:
>Hi Scott,
>
>My valve issue was entirely sloppiness. I had added a port to the
>little HP manifold, and didn't clean the inside of the manifold
>properly after cutting the thread on that extra port. Metal chips got
>into the valves and interfered with proper seating. Two of the valves I
>was able to clean, but one I think got its seat damaged because I was
>just never able to make a good seal on it again. I currently have the
>manifold out of the sub for cleaning, and got a replacement valve on
>eBay. 
>
>I would suggest taking the problem valve apart to see whether something
>has got in there. What you say about storing them open makes sense, and
>I'll do that in the future, but I haven't yet had a valve issue after
>winter storage. I have had issues with the electricals. Last winter a
>speed controller blew after it's first minute or so of spring running,
>and this year I had one that wouldn't work at all for the first few
>minutes but has acted normally once it came on. Maybe the cold made
>some relays "sticky" to begin with.
>
>We must be doing very similar things on our boats right now!
>
>Best,
>
>Alec
>
>
>
>> On Mar 23, 2014, at 12:23 AM, swaters <swaters at waters-ks.com> wrote:
>> 
>> Alec,
>> I remember at the psubs conference in Islamorada you had a
>malfunction on the needle valve from Swagelock. I am preping my sub for
>this season and noticed a air leak. It is comming from one of the same
>needle valves. Did you end up just buying a new one or did you repair
>it? I am thinking based on the way these work they need to be stored in
>the open position. Do you think that is correct?
>> Thanks,
>> Scott Waters
>> 
>> 
>> 
>> 
>> Sent from my U.S. Cellular© Smartphone
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>
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