INSTALLATION AND REPAIR OF
--Seat Warping. In brazed valves, seat warping
INSULATION
results from excess heat applied to the valve body
during brazing.
A basic rule for repair of insulation is that you do
not allow the insulating material to become moist.
Moisture reduces the effectiveness of the material, and
Stuffing Box
in the insulation cause large heat losses, so be sure to
Stuffing box leaks may be remedied by tightening
fill and seal all cavities or cracks. Hangers or other
gland nuts, or by adding rings of packing as required.
supports should be insulated to prevent loss of heat by
Continued leakage may indicate a need to replace all
conduction.
packing in the valve. Do not set up or pack the gland so
All sections of pipe coverings should be tightly
tightly that the stem sticks. Persistent stuffing box leaks
butted at the joints. They should be secured with wire
are usually caused by a bent or scored valve stem.
loops, metal bands, or lacing. Secure the block
Considerable trouble with stuffing box leaks may be
insulation with 18 gauge steel wire and galvanized mesh
avoided if valves are installed with the valve stem
wire, or expanded metal lattice. Use insulating cement
pointing up. Before you alter the position of a valve
to fill all crevices, to smooth all surfaces, and to coat
stem, you should consider convenience of operation and
wire netting before you apply final lagging.
availability of space for removing the bonnet, stem, and
MOISTUREPROOFING is just as important in
disk.
high-temperature insulation as it is in low-temperature
insulation. In the former case, heat is lost because of
EXTERNAL PRESERVATION OF VALVES
evaporation. In the latter case, condensed moisture may
freeze. Either case reduces insulating efficiency and
eventually the insulating material disintegrates. Wet
Now we will discuss the external surfaces of valves
insulation also tends to corrode the piping.
that require painting, with the following exceptions:
Pipe fittings, flanges and valves may be insulated
Valvestem
with the same material used for piping, but they require
different methods.
Valve stem bushing
REMOVABLE INSULATION is usually installed
Valve gland
in the following locations:
Any threaded surfaces
Manhole covers, inspection openings, turbine
For valves that operate above 300F (when the fluid
casing flanges, drain plugs, strainer cleanouts,
c o n t a i n e d is above 300F), two coats of
and spectacle flanges
high-temperature aluminum paint should be used. No
Flanged pipe joints adjacent to machinery or
primer should be used on these high-temperature
equipment that must be broken when units are
valves.
opened for inspection or overhaul (fig. 16-45)
For valves that operate below 300F, primer paint
Valve bonnets of valves larger than 2 inches IPS
should be applied to match the surrounding area. Note
that operate at 300 psi and above, or at 240F and
that all steam valves operate above 300F. Valves made
above
of noncorrosive material (stainless steel, bronze,
All pressure-reducing and pressure-regulating
Monel, and so forth) do not require painting.
valves, pump pressure governors, and strainer
Solid film lubricant conforming to MIL-L-23398B
bonnets
is authorized for valve preservation where temperatures
Some small units of machinery or equipment, such
do not exceed 500F.
as an auxiliary turbine, are located in tight places. It
After you have finished painting, check the valve
would be difficult to install both permanent insulation
to ensure that no paint has inadvertently been placed on
over the casing and removable and replaceable covers
any of the excepted surfaces noted earlier. If so, remove
over the casing flanges. In these situations, the entire
all such excess paint.
insulation may be made removable and replaceable.
16-39