Here in this article, I will cover the gate and diaphragm valve and where they are used in the industry.
GATE VALVE :
Gate valve is known as a sluice valve contains a sliding gate to stop the flow of fluid. They are used as on/off valve rather than throttling valve as throttling is impossible.
Below you can see the figure of the gate valve at the different actuating position. This is a manual gate valve.
Gate valve is normally used for the larger diameter. It is hard to use a gate valve at higher pressure as friction become an issue.
To reduce pressure small valve used in bypass before operation of the gate valve.
They are obstruction less when are fully open, but as shown in the above figure when they positioned in between pressure drops. Also, a partially open gate valve can vibrate due to flowing fluid.
Gate valve are constructed from cast iron, carbon steel, stainless steel, alloy steel, etc.
For the high viscosity fluid and in the solid application knife-edge type gate valve are used.
DIAPHRAGM VALVE :
In the below figure you can see one of the type of the diaphragm valve. When you move handwheel plunger moves which push or take away diaphragm thus allowing flowing fluid to block or pass as you can show in another figure.
Diaphragm type of control valve can be controlled by a different type of actuator out of the most common type of actuator used is a pneumatic type actuator.
Natural rubber, silicon rubber, EPDM, etc. are used for diaphragm material.
Diaphragm type valve can be used in solids, abrasive, corrosive and in slurries, In a corrosive application like in acid or a caustic special type of coated diaphragm is used to protect diaphragm from melting.