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Technical highlights - Pressure
ratings marked on RuB Ball Valves : psi or
CWP?
RuB ball valves are approved
under several international specs, each of
which requires us to put certain markings
on the valve , for example:
- ANSI
Z 21.15/CGA 9.1 requires “A permanent
marking specifying the maximum pressure rating
of ½ psi shall be provided on each valve.”
- AGA
Requirement 3-88 requires “Valves shall
be marked as required in MSS SP 25 --- which
in turn requires “The designation 2G
for a valve rated at 2 psig, or 5G for a
valve rated at 5 psig, shall be shown on
the head, stem, or body.”
- FM
Class 1140 – “Each valve shall
be permanently marked with the following
information:
- Manufacturer’s name
or trademark:
- Nominal valve size;
- Year of manufacture
- Rated working pressure (in
our case 450 or 600 CWP)
To comply with all of these requirements
RuB must put several different pressure
markings on the valves, and it is natural
that these marks should seem to contradict
one another. But in fact it is quite
possible that a particular valve may meet
the requirements of several of these different
specs, and so be permanently marked with
several different pressure ratings.
For example,
the RuB s.195 valves are marked
with 450 CWP, 5G, and ½ psi. And
RuB s.95 valves are marked 600 CWP,
5G, FM 400 WP, and ½ psi.
The ½
psi mark does not restrict the valve to that
pressure. What it means is that the
valve has also been tested and approved for
use in gas appliance connections in buildings.
The tests and design requirements necessary
for that approval include a long list of
safety and efficiency requirements –
for example: operating torque, hammer blow
shock resistance, gas flow capacity, fire
testing, torsional strength when the valve
is screwed onto a pipe, etc. etc. These
requirements are not merely pressure limits.
They are safety issues for a particular type
of gas service, of which pressure limits
are a very small part. But the specification
requires us to mark the valve that way, to
show that we have passed the various tests
for that service.
Henry B. Rose, Technical Director,
RuB Inc. |
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