Valve selection Flashcards
Shut-off valve or?
Block or isolation valve
Can be manual or automatic
Control valve
Example of shut off valve
Gate
Plug
Ball
Gives positive seal in the close position and minimum resistance flow to flow when open
Shut off valve
+available in the widest range of sizes and can be operated manually or by a motor
• have a straight-through flow channel and low
pressure drop when fully open
Gate valve
best used when operated infrequently, as they
require several turns of the valve handle to close
Should not be opened partially as valve seals could be deformed
Gate / Slide
• have the advantage that they only require a
quarter turn to open or close
• often actuated by solenoids and are used
where quick on-off switching is needed
Plug and Ball valve
Normally used flow control valve
Globe valve
Commonly used control valve
Diaphragm valve
Used for the control of gas and vapour flows
Butterfly
Usually globe valves with special trim designs
Automatic control valves
Good flow while keeping
Pressure drops low
Valve must be sized to avoid:
Flashing out of hot liquid
Super critical flow of gases and vapours
are used to
prevent back-flow of fluid in a process
line.
• They do not normally give an absolute
shut-off of the reverse flow.
Non-return valves
depend
on gravity to close the valve, care
must be taken to orient the valve
properly when locating and installing it.
Swing- type check balvo
Two general types of pump
Dynamic
Positive displacement
Example of dynamic pump
Centri
Examples of positive displacement
Reciprocating and diaphragm
Most commonly used type in chem. Indus
Single-stage, horizontal, overhung centrifugal pump
When small flow rates of additive must be added to a process, what will you use?
Positive displacement metering pumps
Pp selection is made on? (2)
Flow rate
Head required
Impeller specific speeds usually lies between
400-20K based on impeller type
Pump impellers classification
Centri or radial
Mixed flow
Axial
Specific speeds between 400 and 4000
Centri or radial
Ns between 4K to 9K
Mixed flow
Ns above 9K
Axial
Ns below 1k, what should be used?
Multi-stagr pump
Used for high head at low flow rate
Reciprocating pumps or Positive displacement
T/F: Selection of pump can be separated from the design of the complete piping system
F
Pressure drops required across control valve will be function of?
Valve design
Control valve and pump should be sized together as unit T/F
T
Control valve pressure drops based on rough guide should be taken at least ____ of the total dynamic pressure drops through the system with a minimum value of ____
30%
50 kPa
A good rule of thumb for each control valve must allow __ kPa pressure drop
70
A valve should be sized for a maximum flow rate of _ above normal stream flow rate
30%
Newtonian liquids using the chart
Constant fluid viscosity
Constant density
Viscosity is a function of shear stress
Non-newtonian
When gas flows through a pipe, the ____ is a function of pressure and determined by pressure drop
Gas density
Liquid-solid mixtures that do not settle rapidly are usually treated as?
Nom Newtonian fluids
If particle is less than 200 microns
Non Newtonian fluids
Gas solid mixture are comnonly encountered in?
Pneumatic converying
Any obstruction to flow will generate ___ and cause ___
Turbulence and pressure drop
Pipe fittings causes an/a ____ in pressure drop
Increase
Pressure loss is due to?
Flow measurement equipment
