Chapter 18. Book 1, introduction to valves.

Question 1

Gate valves

Answer 1

Not suitable for throttle in services because excessive where, due to wire drying occurs on the gate and gate seats. They are used as isolating or stop wells and have very little resistance to flow with a minimum pressure drop through the valve available with rising and non-rising stems for when headroom is limited.

Question 2

Globe valve

Answer 2

The flow of fluid passing through the valve changes direction twice for this reason it is ideal for throttle in regulating flow with minimum wire, drawing and seat erosion, but a disadvantage is it has much more resistance to flow than the gate valve. Another version of a globe valve is the needle valve. It is used for fine control of liquid or gases.

Question 3

Butterfly valves

Answer 3

Correct alignment of this valve is required to prevent binding of the swing through disc come in sizes of one and a half to 200 inches and pressures up to 2000 psi in temperatures up to 1100°C advantages are that it can be used for full flow or throttled It is relatively lightweight easy to operate self cleaning and has very little pressure drop across the valve one fully open, the cost of butterfly valves is considerably less than a gate or globe valve of the same size.

Question 4

Ball valve

Answer 4

Is a quarter turn fully open to fully closed valve requires no internal lubrication and the torque to rotate. The ball is very little has minimal resistance to flow in the fall open position. They are suitable for handling slurries and fluids with a high solid content

Question 5

Plug valves

Answer 5

It is also a quarter turn valve like the butterfly and bowl valve. Most plug valves are lubricated  has a low pressure drop when in the wide open position is a self cleaning valve they can be used in hot water, heating and chilled water systems for flow control. They typically require a hand wrench or valve operator to control positioning.

Question 6

Two types of check valves

Answer 6

Swing type check valve normally used in horizontal position, but can be installed vertically

Lift check valve internally is set up similar to a globe valve where the flow undergoes two changes in direction. There are two lift, check designs, one for horizontal piping and one for vertical piping Dash part which controls how fast the check valve opens and closes is used to cushion the action of the disc in the lift check design .

Question 7

Non-return stop valve

Answer 7

Also referred to as a stop and check valve used on steam boiler outlets and hot water pump discharges to ensure a reversal of flow back into the boiler doesn’t occur. This valve can be used for isolation throttling and prevents a reverse of flow. The valve disc isn’t actually connected to the valve stem, the pressure from the flow pushes the disk up and the stem sets the distance for how far the disk can travel and works as a stopper

Question 8

Pressure reducing valve

Answer 8

Used to reduce the main supply pressure down to a lower supply pressure that can be used by the equipment. Most small systems will have a pressure reducing valve set at 12 to 15 psi. Ideally you should have a minimum of four psi on the highest heating unit in the building to adjust the pressure turn the adjustment screw downwards to increase the spring compression which raises the outlet pressure should be installed with a pressure relief valve that protects the piping system if the pressure reducing valve fails

Question 9

Identification of valves

Answer 9

Accidents have frequently occurred when a valve of the wrong material was installed a valve not properly or clearly identified should be rejected all valves should have the manufactures name service designation like pressure/temperature material designation, like steel or cast-iron valve. May have two ratings a higher rating for water, oil and gas and a lower pressure rating for steam.