Thursday, 24 June 2021 11:32

Non-Return Valves


In 1907 Frank P. Cotter developed a simple valve to allow one-way flow which he patented as a “simple self sealing check valve, adapted to be connected in the pipe connections without requiring special fittings and which may be readily opened for inspection or repair" (U.S. patent 865,631, 1907).

Cotter's original valve patent Cotter's 1907 valve patent
Source: United States Patent Office


In 1916 Nikola Tesla developed an innovative passive device – a “valvular conduit” – with no moving parts designed to allow fluid flow preferentially in one direction. The Tesla Valve, as it is commonly known, was awarded U.S. Patent No. 1,329,559 in 1920.

Tesla's valve patent Patent application for the Tesla Valve
Source: United States Patent Office

Non-return valves and Check valves

The terms non-return valve (NRV) and check valve (CV) both describe a device which operates automatically without external control to prevent fluids from flowing backwards. However, there are differences in the type of valve to which each term refers.

Non-return valves are typically used in systems where prevention of flow reversal is desirable but not critical, for example in pumped heating circuits. In the 1970s, after the publication of a report on the prevention of drinking water contamination using such valves, the term 'check valve' became associated with more high-performance backflow devices. The typical characteristics of check valves are long term durability of their non-return function, suitability for drinking water applications and reliable operation of the valve under strain.

Types of Non-return Valves


A swing check valve or tilting disc check valve has an internal disc secured to a hinge enabling it to swing into two positions in relation to the fluid flow: against the seat when flow reverses, shutting off the flow; or away from the seat, lifted by the forward flowing fluid.

Simple swing check valve

Swing check with spring-loaded disc
Spring-loaded swing check valve

Generally, swing check valves are mounted in a horizontal position but may also be mounted vertically provided that the disc cannot reach the 'stalling position' where it becomes stuck open. The cracking pressure of a swing check valve is the minimum differential pressure between the inlet and outlet at which the valve will open and allow flow; this is primarily related to the weight of the disc. The disc weight also influences the speed with which the valve can properly shut off flow and this can be improved by attaching a spring-loaded lever to the disc.

Swing check valves are called resilient seated when the disc or the seat is equipped with rubber or specialised plastic material to enhance the sealing capability of the valve.

Water Hammer
Water hammer is a common issue caused by swing check valves and occurs when the swing check closes; the abrupt stopping of flow causes a surge of pressure resulting in high velocity shock waves propagating through pipes and valves. Undetected water hammer can place unwanted stress on metal components, potentially damaging pumps, valves, and pipes within the system.

PROS: high flow rates, simple and inexpensive design, simplified maintenance
CONS: water hammer susceptibility, limited sealing capability for non-resilient seated valves



A spring check valve is a device in which a closing member, usually a spring-loaded ball, disc or jumper, is responsible for blocking the flow and keeping it shut. When a ball or jumper is used, the internal geometry of the seal is often conically tapered to increase the sealing area and guide the closing member onto the seal to improve the valve’s performance.

Ball check valve Ball check valve Ball check valve
Ball check valve
Source: Engineering360
Disc check valve Jumper check valve


Because the spring applies constant tension, spring check valves may be mounted in either a vertical or horizontal position without affecting their performance, provided that the pressure of the water column acting on the valve does not exceed its nominal pressure. The cracking pressure, defined as the minimum differential pressure needed between the inlet and outlet of the valve at which the first indication of flow occurs, is related to the weight of the closing member and the spring force.

Spring check valves are often very small, simple and cost effective, and are usually resilient seated, with a disc or seat fitted with rubber or plastic material to ensure superior sealing. Due to the limited flow rate of spring check valves, the water hammer effect is a less common occurrence but can have devastating effects on the closing member if it occurs.

PROS: installation versatility, superior sealing capability, simple and inexpensive design
CONS: limited flow, susceptibility to damage from water hammer



Lift Check Valve
Simple lift check valve

A lift check valve is a device in which the closing member responsible for blocking the flow is a ball or a disc; the closing member can be spring-loaded or be weighted to help keep it shut. Compared with spring check valves, lift checks tend to have a better flow rate but result in more significant head loss due to deflection of the flow through the valve.

PROS: installation versatility, simple and inexpensive design
CONS: increased head loss



Foot Valve
Stainless steel foot valve

A foot valve is a check valve used on the end of a suction line and has an open end fitted with a strainer which prevents debris from entering the line, protecting the pump. As foot valves are usually submerged in a well and not easily reachable for inspection, a robust design, appropriate choice of strainer mesh size and adequate durability are all essential requirements for their success.
Correct sealing of the foot valve is also critical to maintain the working condition of the pump and avoid the entry of air into the suction line (pump priming).

PROS: installation versatility, simple and inexpensive design
CONS: limited flow, potential for blockage due to incorrect strainer size

Zetco Valves

Zetco has been serving the Australian and global market for over 50 years, and we understand how critical reliable quality is to any business operation. Low quality valves and incorrect material selection can result in impactful failures across systems and equipment, resulting in high business losses due to delays and costly replacements.
Zetco offers an extensive range of non-return and check valves designed to meet the specific requirements of our customers, considering all the factors required to achieve optimal performance across a wide range of applications.
To ensure Zetco valves meet the most exacting standards we select only the highest quality materials and undertake rigorous quality testing at all stages of the manufacturing process. With several global patents and ISO 9001 certification, you can depend and rely on Zetco’s quality and ingenuity, knowing we’ve worked hard to get all the details right.

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