EQUIPMENT & SUPPLIES - A safety valve for Field Filtration Unit


                                            February 9, 1977

WATER RESOURCES DIVISION MEMORANDUM NO. 77.51

Subject:  EQUIPMENT & SUPPLIES - A safety valve for Field Filtration
                                 Unit



As a result of WRD Memorandum No. 77.29 announcing the rupture of a
plexiglass filtration unit, we have received some suggestions about a
remedy to the problem.

Some field offices have installed safety relief valves on the pressure side
of the filtration unit.  There are several brand name safety valves
available.  One type that could be used is a Victor Safety Relief Valve,
Part No. 0600-003, with a set relief pressure of 30 psi and sells for about
$4.50 at most gas supply houses.

A safety relief valve can be incorporated into existing filtration units by
installing a tee fitting at the regulation outlet.  The valve should not be
installed directly onto the filter chamber to prevent possible metalic
contamination to the water sample.  Regulators and safety relief valves can
become inoperative due to damage and freezing.  Both should be checked
frequently.  One method of checking is to block the gas outlet with your
finger, slowly increasing the pressure.  The safety valve should pop at its
correct setting.  Return incorrectly operating units to a gas supply house
for any necessary repairs or adjustments.

Since plexiglass deteriorates with age and exposure, it is required that all
pressure filtration units be equipped with a pressure relief devise that
will relieve the internal pressure when it is greater than 30 psi.




                                  Thomas J. Buchanan
Distribution: A, B, S, FO, PO

Key Words:  Field Sampling, Filtration, Water Quality Sampling,
            Safety Value