PART B - VALVES
Gate Valves - Gate valves have a gate in the form of a disk or wedge, which is raised to permit the flow
of fuel and lowered to stop the flow of fuel.
Rising-Stem Gate Valves - Rising-stem gate valves are threaded on the upper end of the stem. The
lower end is attached to a disk. When the hand wheel is turned, both the stem and disk are raised and
lowered. When the valve is fully opened, it will allow pipeline scrapers, poly pigs, etc., to pass through.
By looking at the valve from a distance, you can tell whether or not the valve is open or closed. The
stem of the valve is easy to sabotage. The exposed surface of the upper stem on the rising stem gate
valve should be protected by placing a split, one-inch hose or some similar device around the stem in the
yoke area. A fine film of motor oil can be used to lubricate the thread on the stem. This valve is used in
the pipeline at intervals, at the bottom of long slopes, on both sides of a stream crossing, and at storage
tanks.
Nonrising-Stem Gate Valves - The threaded lower end of the stem on a nonrising-stem gate valve
screws into the disk, thereby raising or lowering the disk while the stem is retained in place by a thrust
collar. The packing gland must be monitored and replaced as necessary.
Globe Valves - Globe valves are used to throttle the flow of product inside a pipeline. This is the same
type of valve used at home on kitchen or bathroom sinks. Packing, disks, and seats will become worn
and will need replacing depending on usage. These valves are used in areas where the throttling of
product flow is desired.
Check Valves - Check valves permit fuel to flow one way only by means of a hinged disk or clapper
which is pushed aside by the fuel when it flows in the desired direction. When flow stops and back
pressure develops, the clapper is pushed against its seat, stopping back flow. These valves are self-
operating and need little maintenance other than tightening the cover nuts regularly. Typically they are
used on the discharge sides of pumps and at pump stations between the suction and discharge lines of
each pump at the pump station. They are also used at the foot of upgrade slopes in lieu of gate valves,
but they must be removed if the line is ever pumped in reverse.
Flow Control Valves (Pressure Reducing Valves) - Flow control valves are activated by pressure. If
pressure in the pilot is great enough to overcome the force of the spring, the excess pressure activates
the diaphragm to throttle the flow in dynamic situations, and in static conditions it will decrease the head
acting against a particular point in the pipeline. These valves require little maintenance beyond checking
the pilot strainer at least every 3 months and inspecting the diaphragm once a year. They are used on
downhill slopes.
Pressure Relief Valves - Pressure relief valves are set to open at certain pressures and are triggered by
a spring. The pipeline is tapped at points which may experience excess pressures under static
conditions. If pressures reach the upper limit set on the valve by the operators, the valve activates by
opening and bleeding fuel off until safe pressures are again reached and the valve resets itself to the
closed position. Typically these valves are used at locations where the pipe is going to a storage tank to
bleed-off excess pressures built up in the line because of heating by the sun under shut down conditions.
These valves should be tested once a year using a reliable pressure gage.
Plug Valves - Plug valves are small, compact valves activated by turning the head of the valve 1/4-turn.
This valve may or may not open to the full diameter of the pipe depending on the type of plug valve
used. As a result, plug valves which do not open to the full diameter of the pipe cannot be used in
portions of the pipeline through which a scraper is designed to pass. This valve can be lubricated in the
open or closed position. Lubrication is done through the lubrication screw at the top by the use of a high
pressure grease gun, or the screw can be screwed down. This valve also has rope-type packing which
must be periodically replaced. Plug valves are commonly used at tank farm manifolds or in places
requiring quick, positive shut-off such as at a scraper launching station.
Additional pipeline components.
Line Strainers - Line strainers catch debris in fuel as it comes down through a basket or strainer and then
passes through the discharge side. The basket has a wire-mesh or screen which catches the debris and
prevents it from continuing to flow downstream and damaging things like pump impeller blades and meters.
The baskets or screens need to be pulled from the devices in which they are installed on a periodic schedule
to remove the debris (once a week). Line strainers are found on the suction side of pumps and meters and
on the discharge side of filter separators.
4-3
QM 5096
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