Page 71 - Boiler_Operators_Handbook,_Second_Edition

56 Boiler Operator’s Handbook

operator that knew the proper procedure for operating ers or never leak, except occasionally. Hmmm… wasn’t
a lubricated plug valve before I explained it. That funny that a statement typical of an engineer?
looking knob that sticks out of the square where you put When isolating systems (see more under lock-out,
the handle isn’t a giant grease fitting that takes an equally tag-out) it’s always advisable to ensure that you’ve
large grease gun. It’s just a screw and when you turn it double protection in the event one of the valves fails or
the movement presses a small amount of grease into the leaks; if there’s another one in the line close it. A vent or
valve. The grease isn’t soft flowing material either, it’s drain between the two valves will release any leakage
very thick and stiff; when you replace it you turn that fit- to atmosphere instead of into the system that’s isolated.
ting all the way out so you can put in a stick of grease. Resilient seated valves (butterfly, ball, globe, and check)
You should give that fitting a quarter turn every can seal initially then leak later if upstream pressures
time you operate a lubricated plug valve unless you’re increase.
operating it several times in a shift, in which case you An important consideration in valve operation is
give it a turn a shift. I’ve had several steamfitters tell me the use of a valve wrench. If you don’t have any valve
that a lubricated plug valve is no good because “they wrenches in your plant then make some and hang them
always leak.” I don’t understand where they get that, it’s where they’re convenient. You don’t slap a pipe wrench
the only valve that you can stop leaking in service. When on a valve handle to open or close the valve. I’ve been in
you turn that plug screw you’re driving that stiff grease in many a plant where the chief engineer would fire any-
between the metal parts of the plug valve to seal it. Unless one caught doing it. The pipe wrench is designed to grip
nobody has operated the valve for years, so the grease a pipe by cutting into it; using one on a valve handle will
has hardened and doesn’t flow uniformly into the valve, create sharp slivers and grooves in the handle’s metal
it will always seal. That’s one reason Factory Mutual first which can tear through leather gloves and cut up the
chose the lubricated plug valve for fuel safety shut-off hand of the next person that tries to operate the valve.
service, what we commonly refer to as an “FM Cock” Make some valve wrenches, all you need is differ-
because they should never leak if operated properly. ent sizes of round stock, a vise to bend it, and for larger
With the exception of those lubricated plug valves sizes a torch to heat the metal so you can bend it. Never
all valves do leak. Some soft seated valves can last what put the portion you grip in the vise so it remains smooth.
seems like indefinitely but an operator should always The standard construction (Figure 2-2) includes drilling
be conscious of the fact that a valve can leak and should a hole for a hook for hanging the wrench near the valve
never, even with lubricated plug valves, rely on a valve for use when you need it. Valve wrenches, by the way,
holding right after it was closed. Sometimes indications are not for closing valves, only for opening them. Those
like pressure dropping can give false assurance that chief engineers I mentioned would also ream you out if
a valve isn’t leaking so you should always wait until they caught you using a valve wrench to force a valve
conditions have stabilized, cooled down or heated up as closed.
the case may be, before taking the position that a valve One last comment on operating valves. It’s a mat-
is closed tight. Also keep in mind that zero pressure ter of courtesy that has almost been abandoned since I
measured by a gage at the high point of a system (or a was an operator. When you open a valve you always
gage with a water leg that’s compensated for it) doesn’t close the handle back down one half, then back one
reveal the pressure at the low point of a system which quarter, turn. That way anyone coming along behind
could have several feet of static fluid pressure on it.
A system isn’t down and without pressure until
all the vents and drains have been opened and, to be
absolutely certain, the lowest drain valve passed some
fluid when it was opened (to prove it really was open
and the connecting piping wasn’t clogged) and, finally,
no fluid is leaving it. If there’s a possibility of gas lighter
than air entering the system (like natural gas) test for
it at the high point vent and a high point closest to the
potential source of that gas before declaring a system
isolated. Also, don’t count on a valve holding if it held
last time. I’ve had many experiences with random leaks
through valves; they leak one time and not several oth- Figure 2-2. Valve wrench