Flowserve Vogt Forged Steel Gate - Manual (Page 25)

Flow Control
Vogt Valves
FCD VVENIM2000-02 Forged Steel Gate, Globe and Check Valves 25
5
Operation and Maintenance
5.1 Introduction
An industrial valve, reasonably matched to a particular service ap-
plication and properly installed in a piping system, can be expected
to have a long service life with a minimum of attention. Unlike totally
passive components such as pipe fittings, vessels, etc., valves are
a special kind of “machinery” having moving and wearing parts.
The satisfactory performance of these working parts depends on
the long-term preservation of various highly finished surfaces.
Therefore, it is important to give adequate attention to the specific
requirements for proper operation and reasonable maintenance of
all valves throughout their service life.
5.2 Operation – Manual Valves
Most valves are actuated manually by causing rotational movement
of a handwheel, wrench, handle, etc. Care is required to assure that
such movement is in the correct direction, is not too fast or too slow
and is applied through the proper distance. The terminal positions,
open and closed, have important functional significance. This is
particularly true in the closed position where the internal closure
element (disc, plug, gate, etc.) must be correctly positioned in rela-
tion to the seat to assure a positive seal.
Check the handwheel jamb nut to ensure that it is tight. After instal-
lation, periodically check the nut to ensure tightness.
Valves in which the closure element moves to and from the seat,
such as in globe, angle, and wedge gate valves, depend to some
degree on the mechanical force of the stem holding the closure ele-
ment against the seat to make and maintain a tight shutoff. This is
most important if the line pressure to be shut off acts on the closure
element in a direction so as to push it off the seat. When globe
valves are installed so that the line pressure then acts in the same
direction as the stem force and also in wedge gate type valves, the
line pressure then acts to increase the seating load, making valve
stem loading less critical. However, substantial stem force will still
be required at low line pressures. The stem force may even be more
important at low line pressures than at high line pressures.