Originally, the diaphragm valve was developed for use in non-hygienic applications. Later on the design was adapted for use in the bio-pharmaceutical industry by using compliant materials that can withstand sanitizing and sterilizing methods.
There are two main categories of diaphragm valves: one type seals over a "weir" (saddle) and the other (sometimes called a "straight-way" valve) seals over a seat. The main difference is that a saddle-type valve has its two ports in line with each other on the opposite sides of the valve, whereas the seat-type has the in/out ports located at a 90 degree angle from one another. The saddle type is the most common in process applications and the seat-type is more commonly used as a tank bottom valve but exists also as a process valve. While diaphragm valves usually come in two-port forms, they can also come with three ports and even more. When more than three ports are included, they generally require more than one diaphragm; however, special dual actuators can handle more ports with one membrane.
Diaphragm valves can be manual or automated. Their application is generally as shut-off valves in process systems within the food and beverage, pharmaceutical and biotech industries. The older generation of these valves is not suited for regulating and controlling process flows, however newer developments in this area have successfully tackled this problem.
In addition to the well known, two way shut off diaphragm valve, other types include: three way zero deadleg valve, sterile access port, block and bleed, valbow and tank bottom valve just to name a few.
Actuators
Diaphragm valves can be controlled by various types of actuators. The most common diaphragm valves use pneumatic actuators; in this type of valve, air pressure is applied through a Schrader valve which raises the diaphragm and opens the valve. This type of valve is extremely quick and as such is one of the more common valves used in operations where valve speed is a necessity. air cylinder
Hydraulic diaphragm valves also exist for higher pressure and lower speed operations. Some diaphragm valves are also controlled manually.
Body materials
Steel type:
Cast Iron
Ductile Iron
Carbon Steel
Stainless Steel

Plastic cone valves and plastic faucet valves drip, freeze inside, and clog with sediment the easiest. Plastic threads are very easy to cross when you wish to attach a garden hose to the drain valve. Even after opening a plastic valve one time, using it and closing it back up, the valve may drip. To remove the plastic cone valve, unscrew it from the water heater by turning it counterclockwise while pulling it out. Six turns will probably be sufficient. Then turn clockwise and keep pulling. Wrap teflon tape around the protruding nipple. Now install the brass ball valve. In order to avoid being sprayed with water while installing the new drain valve, first cut off the water supply at the cold water inlet near the top of the water heater. It is the pipe on the right side as you are facing it. Now open a hot water tap somewhere inside the house; any sink will do. Make sure the hot water tap is closed once water stops flowing through. That'll keep any air from entering the lines.This relieves pressure off the lines and will allow the drain valve to be replaced without emptying the water heater. Make sure nobody is using any water while you are replacing the drain valve. Also turn the gas to pilot or pull the electrical plug if electric. plastic machinery