[labnetwork] DCS excess flow

[Carsen Kline]

Dear Colleagues,

Here at SNF we've been experiencing repeated faults of the excess flow 
switch on our DCS cabinet, which is about five years old and has behaved 
well until recently. When speaking to our vendor about the possible 
causes and remedies, they told us that they typically don't install 
excess flow switches - or regulators - on DCS cabinets, and that they 
would happily send us a jumper to bypass the switch.

My first thought is: That doesn't sound like a good idea, but maybe I'm 
paranoid. There was an excellent discussion here back in Jan/Feb 2015 
regarding heat tracing of DCS lines, and so I'm turning to you to help 
educate me on the pros and cons.

Do you have an excess flow switch? Regulator? Were these optional when 
you spec'd your cabinet? If you don't have an excess flow device, do you 
have any other engineering controls or fail-safes to prevent emptying of 
the cylinder out of a broken line?

Our setup is:
15 lb or 30 lb bottle of DCS in auto crossover cabinet (maximum of 45 
lbs allowed on site per Homeland Security regulations)
0.020" RFO
Cylinder jacket with water circulating at 21C (our vault temperature 
varies throughout the year from 35 to 100 degrees)
Regulator fully open, cylinder and delivery pressure 6 psi
Excess flow switch
Heat traced line approximately 200' from cabinet to point of use

Many thanks for your input.

Best regards,

Carsen

-- 
Carsen Kline
Lab Operations Manager
Stanford Nanofabrication Facility
Paul G. Allen Bldg 131
Stanford, CA  94305
(650)724-8214
carsen at stanford.edu
http://snf.stanford.edu