YARWAY HARDSEAT AND SEATLESS TANDEM BLOW-OFF VALVE SERVICE AND
OPERATION MANUAL
How to operate and service hardseat and seatless unit tandem blow-off valves
The hardseat inlet valve is mounted in a one
piece forget steel block body with the seatless
discharge valve. The valve has a cone seat and
disc design with a metal-to metal seat. The
beveled end of the disc has wearing surfaces.
This 600 psig valve has a lip on the end of the
disc which checks wire drawing and protects
bearing faces against the cutting action of
blow-down.
The seatless valve is a sliding-plunger type.
When open (plunger raised), blow-down
discharges through ports in the lower gland
and plunger. The slotted plunger head slides
on guides in the valve yoke, preventing turning
of the plunger. When the valve is closed, the
shoulder of the plunger contacts with the upper
gland, forcing it down and compressing the
packings above and below the port as the wheel
is tightened.
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OPERATION
This valve is designed so that the blowing valve,
nearest to the boiler, will have flow entering
below the seat. The blowing valve, installed
next to the boiler, should be opened last and
closed first; the sealing valve, furthest from the
boiler, should be opened first, closed last. Both
valves partly opened. Close the seatless valve
with a hard final turn of the hand-wheel to get
the full benefit from automatic tightening of the
packing.
CARE OF VALVES
Since these valves are typically used in severe
service applications (e.g. boiler blow-down
service, boiler drain service) they sould be
included in a regular preventive maintenance
program. It is recommended that valves
operated on a daily basis (blow-down) be
serviced at least every six (6) months. In
frequently operated valves should be serviced
every twelve (12) to eighteen (18) months.
INSPECTION
Valves should be examined externally and
internally. External examination involves
opening the valve closest to the boiler keeping
the sealing valve closed. The complete external
pressure boundary should be examined
thoroughly for leaks. Subsequently, after the
boiler is shut down, the inner valve (i.e.body and
trim) should be examined for any deterioration.
Chapter 11 of the second edition of the
Instrument Society of America´s Control
Valve Handbook is recommended as a good
source for information on valve maintenance
and reconditioning practices.
LUBRICATION
Keep both valves well lubricated. A fitting
(2A) is provided on the seatless valve yoke for
lubricating the ball thrust bearing (11) and the
stem collar. Both areas should be lubricated
every six months. This fitting is compatible with
an Alemite No. 7585 gun. A high temperature
grease equivalent to Texaco Regal AFB2
should be used. Stem threads should be kept
well lubricated Antiseize compound similar to
Never-Seez NS165 should be used.
WARNING
Hot discharge from this product may cause severe
burns. Discharge must be piped away or directed
so that persons in the vicinity are not endangered.
This product must be isolated, vented and cool to
the touch before repairing or inspecting.
