Internals Parts of the Gate Valve
Valve professionals often refer to the term “internals” when it comes to industrial gate valves. However, their focus is not the quality but the internals’ withstand ability of poor working conditions like the extreme stress with corrosion. The internals in the gate valve are the stem, the disc seal area, the seat and the upper seal (if any). For bronze and brass valves, their internals are usually built with the same material as that of the body and bonnet.
Cast iron and ductile iron valves have all iron internals, or occasionally, bronze ones. The iron valve with bronze internals is known as the “iron body, bronze mounted” or just IBBM. For its weldability, steel valves can be equipped with a wide variety of internals, such as Stellite, Hastelloy, 316ss, 347ss, Monel and No. 20 alloy.
Most 19th century valves were thread-ended ones, among which the bell threaded valve can be up to 12 inches long. Flange-ended valves became popular afterwards. Nowadays, other connections in use are thread ended, ring ended, Victaulic, Greyloc, and water specialized “mechanical ended” ones.
Structural Designs of the Body / Bonnet
Designs usually yield five different gate body/bonnet connections. They are threaded, union, bonnet bolted, bonnet welded and pressure sealed ones.
The threaded connection is the simplest design applied only for bronze valves, which are relatively cheaper and seldom to be taken down.
The union connection, which is used primarily for bronze valves likewise, is designed to facilitate the maintenance and disassembly.
The bonnet bolted connection is the most common one of the connections and is everywhere in major industrial gate valves. In order to seal the gate valve, gaskets are required inbetween the body and the bonnet in the case of threaded and union connections.
The pressure sealed connection achieves its sealing by means of the medium pressure acting on the wedge-shaped soft iron or the spherical ink gasket between the body and the bonnet. Therefore, the higher the pressure in the body cavity, the greater the force acting on the gasket. It is much lighter than the bonnet bolted one.
The bonnet welded connection is the most common construction for compact steel valves of 1 / 2 to 2 inches with pressure levels between 800 and 2,500 PSI, which is seldom to be taken apart. Similar to the case of the pressure sealed valve, the bonnet welded valve is lighter than the bonnet bolted one.
Above is a detailed introduction to gate valve internals and body /bonnet designs.
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