The difference between gate valves and ball valves

Gate and ball valves can in general be used interchangeably. Both are considered open/close valves and are seldom used for control. (There are some special ball valves that have a characterized flow profile that permit them to be used for control but they are a very special application.) Although some users believe ball valves have a tighter shut off but that is a function of the seat material and the service. Pressure limits are primarily set by the design of the specific valve.

Ball valves may be considered to give better and more reliable leak resistance and therefore specified where this is most critical such as for gas or liquefied gas applications. Ball valves usually can be opened with a quarter turn of the handle except for very large ones that require a gear type or piston operator.

Gate valves are good for isolation and avoiding a fast opening. By examining the cross section of the gate valve it will be seen that when it is fully open it offers very little resistance to flow. Also when it is just about fully closed, all the throttling is done on the bottom of the discs and seats, making for uneven wear by erosion. For these two reasons gate valves are recommended by China valve manufacturer for use when they are either fully open or closed. They offer little resistance when open and are not suited for throttling purposes when almost fully closed. Also note that the internal pressure always forces the downstream disc against its seat. For this reason gate valves only wear on the downstream side. This wear is eliminated by carefully guiding the disc to its seat. The wear is taken up by guides built into the body of the valve which accurately engage machined wings on the discs.

Stainless steel ball valve is for high pressure and gate valve is for low pressure, the gate valves are used for pressure ratings of 2000 to 5000 psi. Both are generally used for shutoff or equipment isolation purposes.

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Many people mistakenly think that using higher seat pressures causes a reduction in the horsepower delivered to the flywheel because higher seat pressures (and also higher spring rates required for high performance) require horsepower to compress the springs. This thinking is simply incomplete! For every valve that is opening and its valve spring being compressed, another valve is closing and its valve spring is expanding. This expansion returns the energy to the valve train and the engine. Many engineering texts refer to this as the "regenerative characteristic" of the valve train by China valve manufacturer.

Adequate seat pressure is necessary to: 1) Insure tight contact between the valve face and the valve seat to seal the combustion chamber and provide proper heat transfer from the valve to the cylinder head. 2) Keep the valve from bouncing on its return to the seat. If the valve bounces, cylinder pressure (power) is lost. Repeated bouncing of the valve is like a hammering action that can result in the head of the valve deforming or actually breaking from the valve stem resulting in catastrophic engine failure. 3) With a hydraulic cam the valve spring must exert enough pressure against the stainless steel ball valve lifter (or lash adjuster) plunger to keep it centered in its travel to prevent "lifter pump-up". When pump-up occurs the valve is held slightly off its seat resulting in a significant loss of power and possibly a misfire. It is this loss of power and misfire that is often misdiagnosed as a fuel system or ignition system problem.

In Summary, always run enough seat pressure to control the valve action as it returns to the seat. Heavier valves require more seat pressure. Strong, lightweight valves require less seat pressure. When in doubt, run slightly more seat pressure not less.