Non return valve

Non return valve

A non-return valve allows a medium to flow in only one direction and is fitted to ensure that the medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow.
There are different types of non-return valves, such as spring-loaded, swing type, and clapper type valves. Non-return valves are for example used with mixing loops in heating and cooling systems to ensure proper operation, and with domestic water systems to prevent backflow. 
Non return valves basically allow the flow to move in just one direction. As a result, they’re also known as one-way valves. NRVs are also considered a kind of two-port valve as they have two openings: One opening is for exiting and the other is for entering fluids. NRVs usually don’t require manual assistance and function automatically. So most NRVs don’t have stems or handles.

Types of Non-Return Valve

  • Lift Check Valve
  • Swing Check Valve
  • Folding Disc Check Valves
  • Tilting Disc Check Valve
  • Stop Check Valve
  • Vertical or In-Line Check Valve

Lift Check Valve

Lift check valves are commonly used for high-pressure service and when the flow has a high speed. In these valves, the piston disc is precisely target-hunting by long contact and the thickness of the walls of the piston and dashpot are approximately equal. Big steam jackets are employed in the piston and on the exterior of the dashpot. This will prevent sticking out because of diverse enlargement. A lift check valve’s seat design can be compared to a globe valve. Usually, the disk is inside a ball or the type of piston. In vigorous fluid service, ball-lift checks are engaged. The top-notch leak-tight trait of these check valves is better than those of swing check valves.

Swing Check Valve

Once the disc in swing check valves shifts to entirely closed or entirely open status, it becomes unguided. There is a variety of different disc and seat designs that are usable for numerous situations. In comparison to metal-to-metal seating surfaces, soft-seated swing check valves are more leak-tight. To achieve higher leak-tight feature, seats are combined with a metal seat ring and resilient insert. As you may know, the seating angle is the angle between the vertical surface and the seat. This angle may vary from 0 to 45 degrees. The larger the seat angles get, disc movement gets more limited and closes quicker, hence loud noises are reduced, making them especially quiet among the types of non return valve.

Folding Disc Check Valves

Folding disk check valves are made in a wafer-body pattern at factories. These valves have soft or exhausting seats that are typically used in gas field services and low-pressure liquid. Its main characteristic is having a lightweight compact structure. This trait makes this valve extremely popular when convenience and acreage are needed. Folding disk check valves are also known as double-disc or split disc check valves.

Tilting Disc Check Valve

There are a number of flaws with the swing check valve that is fixed with the creation of the tilting disk check valve. This valve is particularly designed to be able to open completely. It can also be stable when the flow velocity is low and shut quickly when the forward flow is stopped. The disk of this valve floats within the flow and fluid runs on its top and bottom surfaces. This dome-shaped disk mechanism minimizes the dashpot impact. Among the types of non return valve, these valves are perfect for turbulent, pulsing, and high-speed flows. These features result in the valve’s lift prolonging and cutting back flow-induced dynamic masses on the piping system.

Stop Check Valve

Stop check valves are used either as an isolation (stop) valve which is a kind of a globe or gate valve or as a one-way check valve. Within the usual system operation, these valves are employed as a daily check valve. However, when needed, these valves can be closed by a screw-down stem. This stem is not mounted on the valve disc. When the stem gets entirely screwed down, it can hold the free-floating disc against the valve seat. This process happens even in a globe or a gate valve. These valves have different types including Wye-pattern, angle-pattern, tee-pattern, and inclined pattern. The swing-and-piston lift-disc style check valves are typically operated to stop check valves.

Vertical or In-Line Check Valve

Vertical or in-Line check valves are the types of non return valve that also come in 2 arrangements: In-line ball check valves are used in both horizontal and vertical lines. When used in horizontal lines, the totally guided disc inline check valves should have the help of a spring-assist closure. But when used in vertical lines, spring-assist closure may or may not be supplied. Not only is the spring-assist closure effective in closing the valve faster; it also prevents flow reversal and therefore minimizes loud noises. These valves can be used in pulsing flows such as a discharge line of a reciprocating compressor. Their size is compacted which makes them popular for small areas.

Use of non-return valve

A non-return valve allows a medium to flow in only one direction and is fitted to ensure that the medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow.