Valves come in all shapes and sizes. In addition to the typical valves covered on the Valve Pipeline it is important to note that there are other valve types that exist. This page will provide a quick overview of some of the non-standard type valves.
Plug valves are valves with cylindrical or conically-tapered “plugs” which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug, so that fluid can flow through the plug when the valve is open. Plug valves are simple and often economical.
When the plug is conically-tapered, the stem/handle is typically attached to the larger diameter end of the plug. Plug valves usually do not have bonnets but often have the end of the plug with the handle exposed or mostly exposed to the outside. In cases like that, there is usually not much of a stem. The stem and handle often come in one piece, often a simple, approximately L-shaped handle attached to the end of the plug. The other end of the plug is often exposed to the outside of the valve too, but with a mechanism which retains the plug in the body.
The simplest and most common general type of plug valve is a 2-port valve, which has two positions, open to allow flow, and shut (closed) to stop flow. Ports are openings in the valve body through which fluid can enter or leave. The plug in this kind of valve has one passageway going through it. The ports are typically at opposite ends of the body; therefore, the plug is rotated a quarter of a full turn to change from open to shut positions. This makes this kind of plug valve a quarter-turn valve. There is often a mechanism limiting motion of the handle to a quarter turn, but not in glass stopcocks.
Slightly conically-tapered metal (often brass) plug valves are often used as simple shut-off valves in household natural gas-lines.
It is also possible for a plug valve to have more than two ports. In a 3-way plug valve, flow from one port could be directed to either the second or third port. A 3-way plug valve could also be designed to shift flow between ports 1 and 2, 2 and 3, or 1 and 3, and possibly even connect all three ports together. The flow-directing possibilities in multi-port plug valves are similar to the possibilities in corresponding multi-port ball valves corresponding multi-port valves with a rotor. An additional possibility in plug valves is to have one port on one side of the plug valve and two ports on the other side, with two diagonal and parallel fluid pathways inside the plug. In this case the plug can be rotated 180° to connect the port on the one side to either of the two ports on the other side.
A needle valve is a type of valve having a small port and a threaded, needle-shaped plunger. It allows precise regulation of flow, although it is generally only capable of relatively low flow rates.
A needle valve has a relatively small orifice with a long, tapered seat, and a needle-shaped plunger on the end of a screw, which exactly fits this seat.
As the screw is turned and the plunger retracted, flow between the seat and the plunger is possible; however, until the plunger is completely retracted, the fluid flow is significantly impeded. Since it takes many turns of the fine-threaded screw to retract the plunger, precise regulation of the flow rate is possible.
The virtue of the needle valve is from the vernier effect of the ratio between the needle’s length and its diameter, or the difference in diameter between needle and seat. A long travel axially (the control input) makes for a very small and precise change radially (affecting the resultant flow). Needle valves may be used in vacuum systems when a very precise control of gas flow is required, at low pressure.
Cryogenic valves are used in extreme low temperatures. Cryogenic valves are usually made out of full stainless with specialized elastomers to handle the cold temperatures. Cryogenic valves have an extended bonnet to move the operator away from the cold process that runs through the port of the valve. Cryogenic valves are typically ordered as per a certain specification; but can be tested to BS6364 (British cryogenic standard).
Y-pattern valves are designed to support the full stress induced by the operating pressure. The design also offers increased flow through the valve over traditional globe and check valves.
Non-Slam Piston and Nozzle Check Valves
A non-slam piston check valve is equipped with a counterweight, or other mechanism (hydraulics), to control the closing time of the valve.
Nozzle check valves (commonly referred to as Noz-checks) have a spring-assisted disc which moves axially with a short displacement to open. The design works to give a streamlined flow path with a venturi effect through the valve, resulting in a low pressure drop. When flow is reduced the disc reacts immediately limiting back-flow. The spring-load, low mass disc and short displacement results in a quick response.
Both of these check valve designs are non-slam meaning they are specifically designed for fast-reversing systems where back-flow is a constant concern. Non-slam valves work to minimize water hammer damage, minimize pressure loss, and protect rotating equipment from damage due to flow reversal.
Actuators are used for the automation of industrial valves and can be found in all kinds of technical process plants: they are used in waste water treatment plants, power plants and even refineries. This is where they play a major part in automating process control. The valves to be automated vary both in design and dimension. The diameters of the valves range from a few inches to a few meters.
Depending on their type of supply, the actuators may be classified as pneumatic, hydraulic or electric actuators. The classification indicates what is required to operate the valve. Pneumatic requires air, hydraulic requires a liquid (typically water/oil), and electric needs electricity.
Actuators are mounted onto the valve in lieu of a lever, gear operator or hand-wheel. Brackets are typically required that work to match up the bolting of the ISO pad (surface where operators are typically located) on the valve to the actuator. An adapter then fits inside the bracket to connect the stem of the valve to the mechanism of the actuator that opens/closes.
Actuators are set to be “fail-open” or “fail-close” which means to move the valve to open/close when certain conditions are met. Actuated valves can be used as ESD’s (emergency shut-down valves) to close automatically when certain bad conditions are met or actuated valves can be used to automate processes (in lieu of manually opening/closing valves)
Actuators are sized according to the torque(amount of pressure) required to open/close a valve. Valves have a break torque (amount of pressure needed to open the valve), and a re-seat (amount of pressure needed to close the valve). Actuators are typically sized with a safety factor ensuring that an actuator strong enough to handle the torque is used.