Sealed transmitter on crude oil


Thread Starter



I have an application where pressure transmitter will be located at the outlet of crude oil pump. The viscosity of crude oil is 6,7 cp and temperature is 90 deg c. Can anybody guide me whether pressure transmitter shall be with diaphragm seal or without diaphragm seal? What are the criteria for deciding whether to use dia.seal? Is it decided on viscocity? And above what number of viscocity is dia. seal required?

Rezabek, John

Dear Anonymous,

My guess is you want the seal because an ordinary tubing/"impulse line" installation would plug up. It is what is sometimes called a "dirty" service. In a "clean" service, the viscosity can be quite high and it makes no difference - no diaphragm seal is typically used. The "fill fluid" of many diaphragm seals is itself a viscous silicone oil,
e.g. DC 200.

The other instance where I've seen diaphragm seals used is where the process fluid is very hazardous (toxic, explosive) and there's concerns about potential hazard to instrument techs & operators.

John Rezabek

Shoaib Pervaiz

Dear Anonymous,

No, the diaphragm sealed transmitter is chosen when the fluid is extremely corrosive. It does not depend on the viscosity of fluid for me. You can use simple transmitter rather than diaphragm sealed type transmitter.

Shoaib Pervaiz
UEC Pvt. Ltd
Dear Anonymous,

For me the most important thing is avoid plugging in the tubing. Therefore, I considered that if not diaphragm seal is chosen, you must use some type of seal (like glycerin) in order to avoid tubing plugging, maybe. Other good practice is to add steam tracing only in the process tap for to keep this part hot, I mean only in the block valve near to the pipe, not in the complete tubing. This is when you are using seal but, if you aren't using glycerin and the complete tubing is filled with the liquid process you must to put steam tracing in the complete tubing...