|
During any practical hands-on exam you can see people going over
the test procedures in their head, time after time, to ensure
they don’t leave out any steps along the way.
Sometimes, it’s the exact opposite that happens.
People actually add steps that don’t exist.
This can lead to disaster. With very few exceptions,
people do the Reduced Pressure Principle Backflow Prevention Assembly
(RP) test first during hands-on testing. It’s probably the test they are most familiar with since RPs
make up the lion’s share of what’s out there.
As a matter of fact, I have yet to go through a proctoring
session without at least one person saying they haven’t tested
a double check (DC) or a PVB (pressure vacuum breaker) since their
last hands-on exam.
Getting
back to the RP, during the test procedures, there are several
points where one can get in trouble.
One such point that seems to cause more than its fair share
of problems for people is during test No. 2; testing the second
check valve.
The
procedures ask you to:
Re-establish
a normal pressure in the zone
“bleed
from the low side”, then
supply
high side pressure behind check valve #2.
If
the gauge does not drop to the relief valve opening point check
valve #2 is recorded as closed tight and you move along.
It’s at this point that some people get an overwhelming
urge to close the by-pass control valve that is allowing high
pressure to go behind check valve #2.
BIG, BIG MISTAKE!
Without
the supply of high side water to the #4 test cock, your readings
may be erroneous. Instead
of getting the actual pressure drop across check valve #1, you
will again be looking at the apparent pressure drop across check
valve #1. Sometimes
people will remember and reopen the by-pass control valve after
re-establishing for the first time.
This too is a mistake; it does not correct the error.
This merely repeats the first test of check valve #2 and
leaves you with possible disc compression.
Your reading could be improper, and the proctor will view
this as an error. The
remedy is simple – once you open the by-pass control valve and
test cock #4, don’t touch it again until the test
is over.
From
that point on the test is very simple if you follow the procedures.
Open the low bleed to re-establish, close the low bleed and record
the reading on your gauge when it stabilizes as the actual reading
for check valve #1. The lesson here is “Think, but don’t overthink.
Don’t add steps that aren’t there.”
When
the nerves take over, strange things can begin to happen.
Remember to remain calm, stop and take a couple of deep
breaths, reengage the brain and you should do just fine. Good luck - and happy testing.
|
