leaking NPT joint on a rotary pump
leaking NPT joint on a rotary pump
(OP)
Hi guys,
I've got a small stainless steel rotary pump which has 3/8" NPT female threads and I'm trying to mount some 3/8" NPT male - 3/8" BSPP adapters (SS as well) on it. I've tried teflon tape but no matter what I do I can't remove a leak from one of the adapters. I've tried various torques, various amounts of teflon tape and still one adapter leaks from the NPT thread. The manual for the pump says that use of pipe dope should be avoided, but I'm seriously considering using Loctite 542 on those threads as I'm sick of disassembling the connections to re-do the joints.
Oh and yes I agree that PTFE tape shouldn't be used on pumps, but the manual says to use that instead of pipe dope. Not sure why to be honest.
Anyone has any ideas?
Regards,
Tom
I've got a small stainless steel rotary pump which has 3/8" NPT female threads and I'm trying to mount some 3/8" NPT male - 3/8" BSPP adapters (SS as well) on it. I've tried teflon tape but no matter what I do I can't remove a leak from one of the adapters. I've tried various torques, various amounts of teflon tape and still one adapter leaks from the NPT thread. The manual for the pump says that use of pipe dope should be avoided, but I'm seriously considering using Loctite 542 on those threads as I'm sick of disassembling the connections to re-do the joints.
Oh and yes I agree that PTFE tape shouldn't be used on pumps, but the manual says to use that instead of pipe dope. Not sure why to be honest.
Anyone has any ideas?
Regards,
Tom





RE: leaking NPT joint on a rotary pump
RE: leaking NPT joint on a rotary pump
might be a different number in the US/UK? This is the stuff I was talking about:
http
I've removed the pump from the motor (it's a magnetically coupled pump) and it turns out there's a kink in the NPT thread on the pump. It rips the teflon tape when it's being screwed in and that's why it leaks, everytime in the same place. I guess a sealant would take care of it, but:
- the 542 product is not so great for SS, only 35% strength compared to normal steel.
- I'm worried about the mess it leaves when you unscrew the fitting. Just had one fitting previously sealed with 542 loosened up and it was quite hard to clean out the female thread on that joint (before resealing). I guess it would be even harder on the pump as the hardened bits can fall inside and damage the pump.
Just as a side note the system will run at around 9bar, 20*C, so perhaps I don't really need too much strength on the joint?
Regards,
Tom
RE: leaking NPT joint on a rotary pump
RE: leaking NPT joint on a rotary pump
nope no way to correct that as I haven't got the tools. Plus it would probably be quite tricky without getting anything inside the pump.
Regards,
Tom
RE: leaking NPT joint on a rotary pump
Good luck,
Latexman
RE: leaking NPT joint on a rotary pump
yup definitely NPT, it even says so in the manual. I'm still not sure why the manufacturer of this pump (Fluid-o-tech) doesn't recommend liquid sealants.
Regards,
Tom
RE: leaking NPT joint on a rotary pump
Ted
RE: leaking NPT joint on a rotary pump
Our pipe sealant of choice for the pump side is X-pando sealant/dope. Something to keep in mind X-pando will make a joint a little hard to break but it can be done. This is a plus in most of our pump systems since we will try other sealants on the make and break joints.
http://www.xpando.com/pjcfaq.html
RE: leaking NPT joint on a rotary pump
yes there is a small kink/crank in the top part of the thread which is what causes the tape rip and leaks. I guess there's no other way than liquid sealant, although I will wait and see what the company technician says.
Regards,
Tom