Hi All,

I'm looking for the typical applications for a diaphragm seal (chemical seal).

I have a couple of Pressure transmitters on a line for an open drain system. The fluids are not particularly corrosive and wouldn't fall under the usual use of a diaphragm seal. However, there most likely will be debris carried along these lines.

So, my question is, do diaphragm seals protect the instrument from debris and should they be used for this reason?

Many Thanks
Max.

 

The remote seal's diaphragm is large, thin and vulnerable. It is not designed for mechanical protection, like you say, it's for isolating a corrosive medium from the transmitter, as you mentioned.

It is conventional practice to connect a pressure transmitter to the 'process' pipe with an isolation valve and a length of pipe or tubing - an impulse line.

I would rely more on the small diameter (1/4", 1/2") impulse line to protect the transmitter from debris because the impulse line is dead headed. There's no actual flow through the impulse line unless the xmtr has a process head equipped with a vent used to purge the impulse line during commissioning or maintenance.

 

Hi MaxL19,

We have a lot of diaphragm seal pressure transmitters installed in many different services.

The selection criteria are typically;
* Process media scaling / blocking - small impulse tubes & transmitter ports block quickly and can be tricky to clean. Fine slurries are our main application for diaphragm seals - normally 50mm to 100mm sizes.

* Purged DP flows not suitable - i.e.; process cannot accept air/water/nitrogen etc contamination

* Process media unstable away from measurement point (i.e.; liquid sulphur - cools very quickly in an impulse tube!)

* Vessel under vacuum & DP level - less leak points in a flanged diaphragm seal vs tubed (maybe this is just me ...)

We don't generally use diaphragm seals specifically for corrosive materials.

Providing the process is "clean" liquid or gas (i.e.; 99% H2SO4 behaves beautifully, as does H2S gas ...) - a standard pressure transmitter is perfect.

Also - Vendors will also offer you rugged "ceramic" diaphragms - similar advantages to diapgram seal - although the places I have trouble with diaphragm seals would eat a ceramic diaphragm in seconds.

So, to answer your question, do diaphragm seals protect the instrument from debris (I read slurry) and should they be used for this reason?
YES. Use them where an impulse tube will block.

But as David_2 noted - diapgram seals are fragile and will not tolerate much abuse. Put them in a dead leg / nozzle - far enough back to protect them from sharp & pointy objects and high velocity erosion. Failing that - they are generally cheaply repaired (Benney do ours).

 

As peterb said, YES. You should consider adding a drip ring = flushing ring.

> So, my question is, do diaphragm seals protect the instrument from
> debris and should they be used for this reason?