by GATE VALVES
There are two main types of gate valves used in the process system:
Rising stem gate valve.
Non-rising stem gate valve
The valve disc in a gate valve is a wedge shaped disc or gate.
It is attached to the end of a threaded stem. The gate fits into
a wedged shape seat in the valve body to stop flow through the valve.
Turning the handwheel raises and lowers the valve disc. When the
valve is fully open the gate is positioned above the passage in
the valve body. This allows full flow in both directions through
the ports. There is little or no restriction and no pressure drop
across the valve.
When the gate valve is fully closed the gate fills the passage and
it stops the flow through the valve completely. Gate valves are
only used in the fully open or fully closed position to start and
stop flow. You must turn the handwheel to many times to move the
valve to the fully open or fully closed position.
RISING STEM GATE VALVE
Large gate valves normally have rising stems. When the handwheel
is turned the stem rises out of the valve bonnet through the handwheel.
The stem shows the position of the valve disc and shows if the valve
is fully open or fully closed. In small gate valves the wheel and
stem may rise together.
The threaded part of the stem is above the valve body. It is not
in contact with the fluid flowing through the valve. This type
of valve has less corrosion problems. The rising stem gate valve
requires more space and more head room.
NON RISING STEM GATE VALVE
Some gate valves have a non rising stem. The stem does not come
out of the valve body. The valve disc moves up and down the stem.
With this type of gate valve there is more chance of corrosion as
the valve stem is in contact with the liquid flowing through the
valve. This type of valve is used where there is not enough space
above the valve for the stem to rise out of the body.
Gate valves provide a good seal against flow. For this reason they
are normally used as isolation valves in high pressure hydrocarbon
pipelines. The gate valve is the most commonly used valves in the
petroleum industry.
If the gate valve is partially closed there may be vibration.
This can cause noise and possible damage to the valve disc and
the seating surfaces. For this reason gate valves should only
be used for throttling (restricting flow) in an emergency.
Three main types of gate designs for gate valves are:
Solid Wedge Gate.
Split Gate (parallel disc).
Flexible Gate
SOLID WEDGE GATE
The solid wedge valve disc was the first type that was used in gate
valves. It does not allow for expansion or contraction of the valve
body and stem material with large temperature changes. This type of
wedge is not used in high temperature processes where there is thermal expansion
and contraction of the valve body
SPLIT GATE
The split gate valve disc is split up the centre. This allows the
element to expand or contract. Therefore, the disc has a better
fit in the valve seat over a wide range of pressures and temperatures.
The wedge can adapt itself to small amounts of distortion caused by seat wear
or piping strain.
FLEXIBLE GATE
Like the split gate valve disc the flexible gate valve disc is
split up the centre. This allows the element to expand and contract
and to give a very tight seal in the valve seat over a wide range
of pressures and temperatures. This type of wedge is used in high
temperature processes
There are two main types of gate valves used in the process system:
Rising stem gate valve. Non-rising stem gate valveThe valve disc in a gate valve is a wedge shaped disc or gate.
It is attached to the end of a threaded stem. The gate fits into
a wedged shape seat in the valve body to stop flow through the valve.
Turning the handwheel raises and lowers the valve disc. When the
valve is fully open the gate is positioned above the passage in
the valve body. This allows full flow in both directions through
the ports. There is little or no restriction and no pressure drop
across the valve.
When the gate valve is fully closed the gate fills the passage and
it stops the flow through the valve completely. Gate valves are
only used in the fully open or fully closed position to start and
stop flow. You must turn the handwheel to many times to move the
valve to the fully open or fully closed position.
RISING STEM GATE VALVE
Large gate valves normally have rising stems. When the handwheel
is turned the stem rises out of the valve bonnet through the handwheel.
The stem shows the position of the valve disc and shows if the valve
is fully open or fully closed. In small gate valves the wheel and
stem may rise together.
The threaded part of the stem is above the valve body. It is not
in contact with the fluid flowing through the valve. This type
of valve has less corrosion problems. The rising stem gate valve
requires more space and more head room.
NON RISING STEM GATE VALVE
Some gate valves have a non rising stem. The stem does not come
out of the valve body. The valve disc moves up and down the stem.
With this type of gate valve there is more chance of corrosion as
the valve stem is in contact with the liquid flowing through the
valve. This type of valve is used where there is not enough space
above the valve for the stem to rise out of the body.
Gate valves provide a good seal against flow. For this reason they
are normally used as isolation valves in high pressure hydrocarbon
pipelines. The gate valve is the most commonly used valves in the
petroleum industry.
If the gate valve is partially closed there may be vibration.
This can cause noise and possible damage to the valve disc and
the seating surfaces. For this reason gate valves should only
be used for throttling (restricting flow) in an emergency.
Three main types of gate designs for gate valves are:
Solid Wedge Gate. Split Gate (parallel disc). Flexible GateSOLID WEDGE GATE
The solid wedge valve disc was the first type that was used in gate
valves. It does not allow for expansion or contraction of the valve
body and stem material with large temperature changes. This type of
wedge is not used in high temperature processes where there is thermal expansion
and contraction of the valve body
SPLIT GATE
The split gate valve disc is split up the centre. This allows the
element to expand or contract. Therefore, the disc has a better
fit in the valve seat over a wide range of pressures and temperatures.
The wedge can adapt itself to small amounts of distortion caused by seat wear
or piping strain.
FLEXIBLE GATE
Like the split gate valve disc the flexible gate valve disc is
split up the centre. This allows the element to expand and contract
and to give a very tight seal in the valve seat over a wide range
of pressures and temperatures. This type of wedge is used in high
temperature processes
