Issues with the threads of Rosemount differential pressure gauges
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Guys, we purchased some Rosemount 3051 differential pressure gauges on-site. The threads on the 5-valve assemblies are of the NPT1/2-14 type. After buying the union fittings, we found that they could only be screwed in 3–4 threads. When we asked the seller, they said that for NPT threads, 3 threads is sufficient for screwing them in. Is that correct? Also, these stainless steel fittings tend to seize easily; is it necessary to apply something or use tape? Thank you all
NPT threads are American standard 60-degree tapered pipe threads. The mating types include \"taper/taper\" and \"straight/taper\"; it depends on the type of mating you use. Turning them in 3-4 threads should not pose any problems, but it mainly depends on the pressure applied. As for Teflon tape, it depends on the operating conditions and environment in which they are used. If the thread fit is not good enough to prevent leaks, it is acceptable to use Teflon tape or gaskets. Using tape just because you’re afraid of it “biting through” seems pointless.
For the tapered threads of the NPT, in order to achieve better sealing, Teflon tape or liquid sealant can be used for sealing; the exhaust ports on Rosemount valve assemblies are also sealed with Teflon tape, so using Teflon tape is a viable option.
It’s best to apply some anti-galling agent to stainless steel, so it won’t be prone to galling
Did you buy your card connector from a small manufacturer, which is why it’s not standard? This has also happened in our company before; it’s possible to have the manufacturer fit them when purchasing the watch, or there are specialized manufacturers that produce qualified coupling fittings. The NPT usually doesn’t require tape, but you can use it if you want to seal it.
NPT threads use thread sealing, provided that they are not of non-standard type or manufactured by small factories. Just tighten it; the threads provide sealing, so tape is not needed. Unlike M20 threads, it does not require gaskets or tape for sealing
From our experience, according to the specifications for the NPT, tape is not required, but we usually wrap some around it. As for how much goes into the NPT, there are also shorter ones. There is no such problem with the differential pressure gauge; I’m not sure which interface you are using. It’s best to buy Swagelock ones.
This post was last edited by Wu Jun on 2020-6-30 at 17:47. NPT1/2-14: The designed threading length is 4 and a half turns; what you bought is pretty much correct
What you buy is definitely suitable; the use of NPT threads in design is precisely because of their excellent sealing properties – there’s no need to use tape or gaskets. Many people, out of habit, like to wrap some tape around them, but normal tightening is sufficient to ensure proper sealing without the need for excessive force.