19 Dec

Needle Valves- How Are They Different From Flow Control

needle-valves-how-are-they-different-from-flow-control

Needle valves are fittings which are designed with a slender and tapered point at the end of its valve stem. This is the valve’s stem which is actually lowered right through the seat, to block or restrict the flow.

Needle valves are used to ensure that the fluid passes through the valve, and actually turns 90 degrees before it passes through an orifice which serves as the seat. This seat comes with a rod having a cone shaped tip. The valves are actually used to regulate the actual flow of liquids as well as gases, at rates which are set at a low flow.

The fine threading design of the needle valve stem, along with its large seat area, ensures that precise resistance will follow. These valves are used to control and check the flow of liquid and gases into the delicate gauges of the system, which are at a high risk of suffering damage if subjected to extreme pressure.

These valves are also utilized in industrial equipment, where the flow needs to be brought to a final halt. They are also utilized where a precise adjustment of the flow is considered essential, or wherever a small and controlled flow is needed. These valves can easily be used as both on and off valves, along with the use in a system for throttling service.

Difference Between A Flow Control And Needle Valve

Both of these fittings are used to control and reduce the flow of air in the leg of a pneumatic circuit. This results in slowing down the actuator speed. While the basic function of both the fittings is flow restriction, the main difference is that the needle valve controls the flow of liquid or gas in both directions, while the flow control valve only ensures control in one direction only.

The needle valve is bi directional, while the flow control is one directional only. In both the fittings, there is a finely threaded stem, which allows the gradual adjustment of the quantity of controlled flow, which passes through the valve. This controlled flow enters the input port and travels through the orifice, which is actually sized by the tapered stem, and out through the output port.

The flow control fitting actually features a simple by pass feature, which is then allowed to ensure a rapid and free flow, out from the output port of the fitting, by means of the input port.

Two types of flow control fittings are used for the purpose of selection and placement, within a carefully designed electric circuit and which in turn greatly affects the overall functions of an actuator.

A meter out valve is a very common type of flow control fitting, which is used to control the actual exhaust flow being emitted by an actuator. While a meter in flow is a fitting which is used to restrict the overall flow of actuator. It is also termed as reverse flow control.

Sourced by ekomeri.com

06 Dec

What Is A Plug Valve And When Is It Used?

what-is-a-plug-valve-and-when-is-it-used

We’ve previously discussed how to select specific valves for improving production time and MTBF and thought it would be a good time to review one of the most simple and economical valves available: the plug valve.

Plug Valve Basics

 A plug valve is shaped like a cylinder or cone and can be rotated inside the valve body to control flow of fluids. Plug valves have one or more hollow passageways often placed horizontally to allow ease of flow through the valve when open. The most common type of plug valve is the 2 port model with an open and closed position. The two ports are usually located on opposite sides of the valve with one passageway leading from inbound to outbound and the stem and handle located on the top. A plug valve also uses a quarter turn valve, which is useful where quick and frequent operation is essential. The valve ends can be flanged, hub type, or butt weld.

Plug Valve Types and Their Uses

 Although there are many types of plug valves, there are four general categories, each with their own benefits.

1. Lubricated Plug Valve

 As the name suggests, a lubricated valve uses a lubricant usually made up of a base oil and viscosity improver (like amorphous or fumed silica) that is injected under pressure between the plug face and body seat to reduce friction and seal ports. Valve manufacturers generally recommend lubricant suitable for the process fluid, and the valves often must be resealed after only a few cycles, and in some cases, after every cycle. Considered a high maintenance plug valve, they are often used in applications that have infrequent operations. Lubricated plug valves perform well in processes that utilize fluids which carry mildly abrasive particles such as dirty upstream applications, gas pipeline systems that need bypass valves, and as blow-down valves on valve stations and kicker valves.

2. Non-Lubricated Plug Valve

This plug valve utilizes a tapered or cone-shape that acts as a wedge and presses a polymeric sleeve against the body cavity. The use of the sleeve reduces friction between the plug mechanism and body.  Non-lubricated plug valves are often used instead of lubricated ones in applications where maintenance needs to be kept to a minimum, such special services in sulphur, hydrogen fluoride, or where liquids could be trapped or solidify and potentially jam the valve. However, non-lubricated plug valves are limited by temperature and chemical compatibility of the non-metallic materials they are made of.

The three main types of non-lubricated plug valves are:

Lift-type plug valve

Elastomer sleeved plug valve

Fully lined plug valve

3. Eccentric Plug Valve

The design of this plug valve uses a half plug that is advantageous for applications needing a higher seating force with minimal friction from open to closed position. The torque seated valves also feature improved shut off capabilities. Eccentric plug valves are used for a wide range of flow control and isolation applications including clean and dirty water, sewage, sludge and slurries, air, and other services.

4. Expanding Plug Valve

 This complex plug valve uses multiple components that allow the valve to mechanically expand and give it a true double block and bleed function in one valve. The plug valve uses a mechanism that rotates between the open and closed position and protects both seals from the flow path. During rotation there is no contact between body and seals, and slips expand onto the body seat when the valve is closed to avoid causing any wear or abrasion to the seals. They are often used to prevent product contamination in applications that do not require a double isolation.

In conclusion, plug valves have a number of useful applications, and new technology and designs are sure to give them an even wider variety of applications within many processes. And if you need more information on different types of valves, check out this piece on check valves or the rest of the site.

 

Sourced by ekomeri.com

29 Nov

Installation Guidelines for a Check Valve

installation-guidelines-for-a-check-valve   Check valves are simple devices that allow fluid media (gas, liquid or solids such as sand or slurry) to flow only one way. Typical check valve installations are found in industrial plants, automobiles, plumbing and ventilation systems. Usually, check valve are relatively inexpensive, compared to more accurate control valves. For a given application, the valve body must be able to contain the media and pressure, and the gate action must have a durable service life. Installing check valves is a matter of determining the correct flow direction for the media and ensuring proper fittings for the inlet and outlet port.

Materials
Installing the correct check valve for a particular process means knowing the media the valve will control. Caustic or abrasive media (lime slurries, acids, cement mixes, etc.) require a check valve resistant to severe corrosion; stainless steel or ceramic check valves work well for such applications. A check valve installed to control hot water flow in a plumbing installation can be made from PVC plastic, brass or steel. As long as the valve can handle the heat and pressure of a standard water line, it will work well.

Installation
Installing a check valve is similar in procedure to installing any other valve with one important distinction: direction. The valve must be installed in the media’s flow direction–nothing can move against a closed check valve gate. Check valve manufacturers include on the valve body an arrow indicating proper flow direction.

Incoming and outgoing lines can be connected using clamps, swage fittings (fittings using a collar around the line, with the fitting and the valve stem hydraulically compressed together) or threaded fittings.

Access
Check valves work automatically to eliminate back flow in a process line. There’s no need for manual operation–the valve can be installed in relatively inaccessible locations. Although other valve installations may require clearance for actuators, access to a manual valve shut off or other features, check valves require little maintenance.

If installed as a diversion valve to relieve excess pressure or heat, the check valve gate can be adjusted to respond to specific pressure settings. For example, a check valve can prevent a steam boiler from building up too much pressure or a car’s radiator from rupturing when the coolant fails: the check valve will divert the high pressure media away from the process and avoid catastrophic failure. When pressure and heat amounts remain within operating limits, the check valve will stay closed.

 

Sourced by ekomeri.com

03 Nov

What is a Plug Valve?

what-is-a-plug-valve

A plug valve is a simple type of valve that allows or blocks the flow of a liquid through a pipe. The plug itself is often shaped like an upside-down ice cream cone or a cylinder. A handle on top allows the user to turn the plug valve so it rotates and stops or starts the flow of liquid. A minimum of two holes, known as ports, must exist in the plug for liquid to flow. The ports are located on opposite sides of the plug, and when the plug is turned to the open position it creates a passage for the liquid to flow through.

This arrangement of two ports is known as a 2-port valve. The pipe in which the plug valve is installed has an area for liquid to flow in and another for liquid to flow out. When the 2-port plug valve is turned on, the ports line up with the holes in the pipe and the liquid flows straight through as if the plug valve was not there. Other, more complex plug valves known as 3-way valves allow liquid to flow to a combination of different ports. One port may connect to either of the opposite two ports, or all three may connect at once.

Two major categories of vales exist: stop valves and check valves. Stop valves follow a basic design structure to turn the flow of liquid on and off, or allow partial flow. Check valves, in contrast, allow liquid to travel only one way and often do not have a handle. Plug valves fall into the stop valve category.

Other stop valve types include gate valves and ball valves. Though similar to plug valves, the shape of the parts and how they work to stop the flow of liquid typically determines the specific group they belong to. Regardless of group, stop valves typically control liquid through the use of a handle.

Operation of a plug valve is simple, making it a common valve choice. The user twists the handle and the ports are moved away from the opening in the pipe. In certain valves, a full turn is not required. Quarter-turn valves, for example, only require the user to make a short, quarter turn to stop the flow of liquid. Often, plug valves can lessen the flow without turning off completely if the user turns the valve half-closed but leaves it open wide enough for some liquid to make it through the ports.

Souced by ekomeri.com