NIBCO UL Bronze Gate Valves - Manual (Page 4)

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4
The body and bonnet are held together by threads of the male and female type; male
threads being on the bonnet section and female threads being within the body. There
are no gaskets between the body and bonnet to affect seals. This is strictly a metal-to-
metal seal as required by standards. This general arrangement is used on the Class 125
and is also used on the Class 150 gate valves.
For the union bonnet arrangement the body has male threads, the bonnet has no
threads at all, however, a threaded union nut is placed over the bonnet to fasten it to the
body. The seal between the body and bonnet is also metal-to-metal without a gasket.
Flow through the valve is stopped by forcing the wedge down between the seats of the
body. The wedge is a solid type and is guided through its entire travel by guides in the
body.
The head of the stem on the rising stem version fits into a T-slot in the top of the wedge
to allow sufficient wedge movement for effective seating with the seats of the body. On
the non-rising stem version, the wedge has internal female threads and the stem has
male threads which are left handed to cause the wedge to close when the handwheel is
turned in a clockwise direction and the wedge to rise when it is turned in a
counterclockwise direction.
All valves have back seats between the shoulder of the stem and the valve bonnet. This
is a requirement of standards so that the valve may be repacked while the valve is under
full pressure. CAUTION: This is dangerous and could result in serious injury. It is
not recommended by NIBCO. In addition, standards, organizations, and governing
societies today do not encourage valves to be repacked while the valve is transmitting a
fluid at full pressure and/or temperature.
The stuffing box is formed by the annular space between the stem and the bonnet and is
filled with non-asbestos packing. The packing is compressed in the stuffing box by a
gland bushing and the packing nut drawn down against the packing by turning the nut
clockwise.
2.0 INSTALLATION
2.1
PRELIMINARY INFORMATION
The gate valves should preferably be installed with the stem pointed vertically upward.
However, it is normally acceptable to have the valve stem pointed in a horizontal position
either in vertical or horizontal piping.
Although a gate valve will function satisfactorily in an inverted position it is not generally
recommended because it allows fluids to become trapped in the bonnet cavity resulting
in contamination and inability to fully drain the system. This is critical in water lines
exposed to freezing temperatures.
Valves are shipped in the closed position to prevent damage to the seating surfaces.
There is not internal blocking used for shipment. All NIBCO valves are shipped in
cardboard boxes for protection against exterior damage and accumulation of dust or dirt