Ashford Instrumentation Ltd - Safety Pattern Gauge Selection

Safety Pattern Gauge Selection

At Ashford Instrumentation Ltd we are often asked to supply pressure gauges to meet certain process applications. The following information has been prepared to help our customers understand when safety pattern gauges are required according to the European Standards for Pressure Gauges EN837-1:1998.

Construction

The definition of Safety Pattern Gauges is given on Page 12 of En837-1:1996 Section 9.7.2.

According to the standard, only “S2” and “S3” designs are classed as safety pattern gauges.

Broadly Speaking:

S1 Design - Blow Out Device Only

S2 Design - This design must have passed the Energy Release Test as defined in 10.12.2.2, have a non-splintering window (laminated safety glass or non-splintering plastic) and a blow out back as defined in 9.7.2.3.

S3 Design - In addition to the requirements of “S2”, “S3” gauges must have a blow out back as defined in 9.7.2.3.

Dial Sizes & Construction Constraints

For dial sizes 40mm to 80mm gauges can be manufactured to “S2” without a baffle wall For dial sizes 40mm to 250mm gauges can be manufactured to “S3” with a baffle wall.

For both types the dial to be marked “S” along with the EN Number. Gauges with only a blow out device are classified as “S1”. Both “S2 & S3” designs must have passed the Energy Release Test as defined in 10.12.2.2, have a non-splintering window (laminated safety glass or non-splintering plastic) and a blow out back as defined in 9.7.2.3.

In addition “S3” gauges must have a baffle wall as defined in 9.7.2.4.

When Should You Use Safety Pattern Gauges

EN837-1 Section 9.8 states that gauges for use on oxygen or acetylene should be safety pattern design. Page 4 of EN 837-2:1997 provides a table detailing the type of safety construction required depending on whether the gauge is to be used on liquid or gas (including steam). Broadly speaking:

1. Dry gauges used on a liquid media on any pressure do not require any safety features regardless of gauge diameter.

2. Liquid filled gauges used on a liquid media of any pressure should be of “S1” design regardless of gauge diameter.

3. Dry gauges used on gas or steam with a diameter below 100mm do not require any safety features on ranges 25 bar and below, but should be “S2” on applications above 25 Bar.

4. Dry gauges used on gas or steam with a diameter 100mm and above require “S1” construction on ranges 25 bar and below, and should be “S3” on applications above 25 Bar.

5. Liquid filled gauges used on gas or steam with a diameter below 100mm require “S1” construction on ranges 25 bar and below, and should be “S2” on applications above 25 Bar.

6. Liquid filled gauges used on gas or steam with a diameter 100mm and above require “S1” construction on ranges 25 bar and below, and should be “S3” on applications above 25 Bar.

Important Notes

All gauges used on oxygen, and acetylene should be of safety design regardless of diameter or pressure range.

Glycerine filled gauges should not be used on oxygen or other strong oxidizing process fluids. For such applications highly fluorinated and chlorinated liquids can be used.