Section Three Valves Flashcards
What is the purpose of a valve?
To stop or start flow, or to regulate flow.
Regulation of flow includes:
Throttling, prevention of flow reversal, and relieving or regulating pressure within a system.
There are eight basic valve designs available. Name all eight.
Gate. Globe. Check. Diaphragm. Ball. Butterfly. Plug. Relief.
How should a gate valve be used?
For on or off service either fully open or fully closed.
Why are gate valves either fully open or fully closed?
Because of excessive vibration and wear created in partially closed gates valves are not intended for throttling or floor regulation.
What kinds of gate valves are available?
Solid wedge. Flexible wedge. Split wedge and double desk styles.
What service is the wedge type gate valve used for?
Suitable for air. Gas. Oil. Steam. Water.
When installing either a split wedge or double desk gate valve, the stem of the valve must be in what orientation?
Vertical.
How should a globe valve be used?
Globe valves, unlike gate valves, are used in applications requiring frequent operation and or throttling of flow.
Globe valves are available in three body styles name all three.
Angle body. Y pattern and T pattern. Straight way (most common).
What do angle body valves provide in terms of direction of flow?
90° change of direction.
What angle does the stem of a Y pattern globe valve protrude from the body?
45 or 60°.
The Y pattern globe valve is ideally suited for applications requiring almost:
Full flow in a valve but with the characteristics of a globe valve.
Applications for Y pattern globe valves include:
Boiler blowoffs and services where mud grit and or viscous fluid’s may be encountered.
The main types of globe valves according to their seat arrangements are:
Conventional disk. Plug disk. Composition disk. Needle valve.
Conventional desk globe valves use a what?
Short tapered disk for closure and throttling.
When is a conventional disk globe valve preferred?
When flow conditions have a tendency to deposit coke on valve seats.
How does the plug disc differ from the conventional disc Globe valve?
The plug disc and seat arrangement are longer and more tapered. The longer area of the plug and seat give the plug maximum resistance to flow induced erosion.
Needle valves are designed for small diameter lines requiring what?
Fine throttling of gases, steam, oil, water, or any other light liquid
What service are check valves used for?
Back flow prevention.
The two most common designs of check valves are:
Swing check. Lift check.
How should a swing check valve be installed?
Installed so the swing check valves disc closes positively by gravity.
What are diaphragm valves sometimes referred to and what service are they use for?
Saunders valves. Used to control flow for corrosive services were line content could abrasively affect the valve components And where outside contaminants are not tolerated.
How can most diaphragm valves be classified as? Name both.
Weir type. Straightway type.
Of the weir diaphragm type and the straightway diaphragm type valves which is the most common?
Weir.
Pinch valves are another type of diaphragm valve. what services are pinch valves ideally suited for?
Suspended matter, slurries and solid powder flows.
How should a ball valve be used?
Fully open or fully shut.
Ball valves come in three general patterns name all three.
Venturi port. Full port. Reduced port.
Aside from ball valve patterns they may also be classified by their body styles. What are their body styles?
One piece. Multi piece.
How can a butterfly valve be used?
On off or throttling.
Because of the advances in seating material, butterfly valves have found general acceptance in what services?
Oil, gas, chemical, water, and process fields.
How should plug valves be used?
On off service.
There are two basic types of plug valves available:
Lubricated plug. Non-lubricated plug.
How do relief and safety valves work?
Automatically relieve excess pressure in pressure vessels or piping systems.
In what situation is a relief valve used?
In applications were full discharge of pressure is not required to relieve excess pressure.
How does a safety valve work?
Used to fully relieve pressure in the system of compressible fluids and gases which may cause an explosion went over pressurized.
What is the primary function of a valve bonnet?
To provide for a pressure tight transition assembly from the valve body to the valve stem.
There are four basic stem mechanism designs available for valves what are they?
Inside screw rising stem. Inside screw nonrising stem. Outside screw rising stem. Quick opening sliding stem.
