1. Valves

2. Valves
Valves are devices that control the flow of fluids or gases through a piping system
Valves can provide on-off service only, allow different flow rates, relieve excess pressure , or prevent reversal of flow.
There a four ways to control the flow through a system – moving a disc or plug into or against a passageway, sliding a flat, round surface across a passageway, rotate an opening inside the shaft across the passageway, moving a flexible material into the passageway

3. Valves that start and stop flow
Gate valves – start and stop liquid flow, but do not regulate or throttle flow
A disc is turned into the flow stream
Little drop in pressure when the valve is open because there is little resistance to flow
This valve should only be used in the fully open or fully closed position because partially open can cause disc and seat wear

5. Knife gate valve – this valve is used in slurry and waste lines and other low pressure applications
The sharp edge of the disc is forced closed in contact with a metal or elastomeric seat
The disc can cut through deposits and flow-stream solids like resin slurry or pulp

7. Ball valves – use a ball to start or stop flow
They are rotary action valves
The ball has a hole in it – when open the ball is turned to where the hole is in line with the inlet and outlet – when closed the hole is perpendicular to the openings
Most ball valves are quick acting and only require a 90 degree turn to open or close
They are generally not good for throttling because it erodes from the flow

9. Plug valves – rotary action valves – the stop disc is on the shape of a plug
The disc is solid with a bored passage at a right angle to the longitudinal axis of the plug
The openings of the valve may be different shapes and sizes to regulate flow

11. Three-way valves – installed at the intersection of three lines
They direct flow between two lines and block off the third line

12. Valves that regulate flow
Control and provide accurate flow through a system
Globe
Butterfly
Diaphragm

13. Globe valve – disc can be totally removed or can completely close the flow path
The disc moves perpendicular to the seat which allows good throttling ability
The disc can close in the same direction as fluid flow or against direction of fluid flow

15. Butterfly valve
A quarter turn valve with a plate like disc that stops flow when the outside area of the disc seals against the inside of the valve body
They have a arrow stamped on it to tell the direction of the flow through the valve
They must be installed in the proper flow direction or it will not seal

17. Diaphragm valve
Flow is controlled by a flexible disc that is connected to a compressor by a stud molded into the disc
The valve stem moves the compressor up and down to control flow

18. Needle valves
Make fine adjustments in the amount of fluid allowed to pass through an opening

19. Valves that relieve pressure
Safety valves – used in steam, air, or other gas pipelines – they operate in the closed position until the pressure in the line rises above the preset pressure limit – it will remain open until the pressure drops, then the valve snaps shut
Pressure relief valves – used to relieve pressure in liquid services – when the pressure gets too much, the disc that is attached to a spring rises to release the pressure – when the pressure is released the spring pushes the disc back into place
There is also a pressure relief valve that is called a rupture disc – the disc ruptures when the pressure gets too high – can not be reused

21. Valves that regulate direction of flow
Check valves prevent backflow – only permit flow in one direction Swing check valves – disc that swings open or closed Ball check valve – uses a ball to allow fluid to pass through the valve – not spring loaded Butterfly check valve – two vanes that fold back from a central hinge to open but fold back to prevent backflow

23. Valve actuators
Provide automatic control of the valve or to reduce the effort required to manually operate a valve
Gear operators, chain operators, pneumatic and hydraulic actuators, electric or air motor driven actuators

24. Installing valves
Location is very important – direction of flow, height of the valve, ability to work on the valve