Explosion Proof Pressure Switch for Solvent Vapor Exhaust Duct

Good luck. Teflon is quite stiff. I don't think I've ever seen it in such a low pressure application.

United Electric's J120K-540 has a range of 0.2" to 7.0"H2O but its sensing diaphragm is buna N (rubber) which will not hold up to solvents.

Dwyer does a lot of low pressure switches (magnehelic or photohelic lines), maybe they've got a solvent resistant diaphragm.

An I/S barrier with a field mounted switch could be an alternative to EXP for a simple switch.

I suspect you'll end up with a draft range DP transmitter and have to alarm from its analog output.

Check out Midwest's Model 130 with viton diaphragm and plastic body, switch option in EXP housing.
http://www.midwestinstrument.com/pdfs/bulletins/bul130.pdf

Or the 105 series with bellows actuation (options for EXP switch).
http://www.midwestinstrument.com/pdfs/bulletins/bul105_106.pdf

Is this on an oven/dryer? We coat solvent-based adhesives and dry them in a gas-fired convection oven.

One of the most important things is that we have enough air flow through the oven to keep the solvent(s) below it's/their Lower Explosive Limit.

Do you have a way of measuring the solvent vapor concentration?

To make sure we have enough air flow to accomplish this, we continuously measure the concentration of solvent in the exhaust.

A word of caution; If the exhaust fan stops, solvent concentrations can quickly build to explosive levels. Is this the reason behind needing said pressure switch?

This link will get you started:

http://www.nciweb.net/pressure1.htm

A simple "sail switch" might also work, if made of suitable material.

There ya go again...stealing my brilliant answer!!

Any switch will be compliant if installed as part of an EEx ib system.

Do you think I have to worry about the elastomer on the switch diaphragm if I am "normally" under negative pressure (the exhaust fans running?)

It doesn't matter if the fans are running or not. The answer is still "yes".

Thanks for the suggestions.

Midwest looks close but Toluene will eat every diaphragm material they offer.

Anyone know of a Draft Range PT with teflon or SS diaphragm?

Go for United Electric.

ITT Neo Dyn has a model 142P that has a range that should work. It is not advertised as a DP switch but it has a large SST diapram and a port 1/4" port on the back side you can use to hook up to the low press side and the standard port to the High side. you can get all SST wetted parts except for a oring that can be specifed with Kalrez that should be resistant to your solvent. XP is a standard offering.