26. April 2014 · Comments Off · Categories: Gate valves

Definition

A gate valve, also referred to as a sluice valve, is a valve that opens and closes to regulate fluid flow. A gate valve opens by lifting a rectangular or round gate or wedge, often called a sliding door, out of the fluid’s path to allow it to flow though.

Features 

The distinct feature of a gate valve(made by China valve supplier) is the sealing surfaces between the gate and seats are planar, so gate valves are often used when a straight-line flow of fluid and minimum restric­tion is desired. The gate faces can form a wedge shape or they can be parallel. Gate valves are primarily used to permit or prevent the flow of liquids, but typical gate valves shouldn’t be used for regulating flow, unless they are specifically designed for that purpose.

GATE VALVE

Industry svered

Because of their ability to cut through liquids, gate valves (manufactured by China gate valve manufacturer) are often used in the petroleum industry. For extremely thick fluids, a specialty valve often known as a knife valve is used to cut through the liquid. On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that flow rate does not change evenly with stem travel. Also, a partially open gate disk tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing disk and seat wear and eventual leakage if used to regulate flow. Typical gate valves are designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.

Pressure seal bonnet 

Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 15 MPa (2250 psi). The unique feature about the pressure seal bonnet is that the body – bonnet joints seals improves as the internal pressure in the valve increases, compared to other constructions where the increase in internal pressure tends to create leaks in the body-bonnet joint.

Classification

Bolted bonnet gate valves, pressure seal gate valves; wedge gate valves, flate gate; rising stem gate valve, non rising stem gate valve; API 600 gate valve, API 6D gate valve; cast steel gate valves, forged steel gate valves.

OPtions

Gate valves may have flanged ends which are drilled according to pipeline compatible flange dimensional standards. Gate valves are typically constructed from cast iron, ductile iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels.

Functions 

Gate valves are used in straight-flow fluid systems where a minimum amount of friction is required. Unlike other valves, gate valves are constructed to be used either completely open or closed. If partially open, the fluid velocity can damage the gate valve’s seal and cause leakage.

Relia Valve is a professional China ball valve manufacturer, for high quality cast steel gate valves, forged steel gate valves, globe valves, check valves and ball valves etc.

02. April 2014 · Comments Off · Categories: Gate valves

Difference between Parallel Gate Valves and Wedge Gate Valves

As the names imply, a parallel gate valve has parallel seat faces while a wedge gate valve has non-parallel seat faces. The design standards are also different, a parallel gate valves made by China valve supplier are designed to API 6D, whild wedge gate valves are to API 600 or API 602. The  wedge gate valves are normally regular port, while the parallel gate valves are requested in full port design.

 The wedge gate valve is much more common, it’s typically what you find in a hardware store, you almost never find a parallel gate value there. The advantage of a wedge gate valve is that it is “self seating”, i.e., will shut off flow as tight as you can turn the handle. The flaw with that design is what’s solved by the parallel gate valve—what if there’s some small debris stuck in the seal somewhere? The parallel gate valve in design “pushes the debris” off the parallel seals as the valve is shut. But this works only if the valve is manufactured with high precision, which is why such valves find use in bigger, more costly applications, where reliability of true shut-off is mandated.

wedge gate valve

Wedge gate valves, if free of debris, is more capable of shutting off flows at higher pressures than parallel gate valves. The latter is limited by the machined precision of its parallel seat faces. As a rule, high pressure valves rely on the mechanical pressure that can be exerted on the seal faces by valve operation, and parallel gate valves cannot exert any beyond a certain level by design.

The indstry wedge gate valves and slab gate valves (made by China gate valve supplier) are different. Oil Field Trash cites a parallel gate valve that “by design” has a high pressure exerted on the soft seals, but this cannot be increased with any “turning of the handle”. But to achieve such high seal pressures reliably does require more costly manufacturing design than the simpler wedge gate valve for the same effective pressure holding ability. The essential difference is that the latter wouldn’t work well with fluids commonly used in the oil industry because of the nature of the fouling in the fluids, which was the point of my answer why parallel gate valves have their uses. Extremely high pressure valves depend on mechanical pressure on the seals, that’s just a given. That’s why there are so many different kinds of valves, because it all depends on the application.

In conclusion, when choosing wedge gate valves or parallel gate valves, you need to think about above factors specified above, and you need to clearly specify details when you need to ask for quotation.

By Kevin for Relia valve, professional China valve supplier