Ball Check Valves | For Viscous & Contaminated Media

Check valves: flanged ductile iron and stainless steel

Doppelflgel-Rückschlagventile aus Edelstahl & GGG40 von FERGO

Dual Plate Check Valves

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Frequently Asked Questions – Non-Return Valves

A non-return valve (also called a check valve or backflow preventer) is a purely mechanical device that allows flow in one direction only – it requires no manual or electrical actuation. Its operation is governed entirely by differential pressure:

Forward flow (normal direction): System pressure lifts the flap or disc off its seat against gravity or spring tension, allowing unrestricted flow through the valve
Reverse flow or pressure drop: As soon as flow velocity drops to zero or backpressure exceeds forward pressure, the flap or disc returns to the closed position – under its own weight (gravity closure) or assisted by a return spring – sealing the valve and preventing any reverse flow

Why non-return valves are essential:

Pump protection: Prevents reverse rotation of pump impellers and motor damage caused by backflow when the pump stops
Water hammer prevention: Fast-closing designs (especially dual plate valves with spring return) close before reverse velocity builds up, eliminating destructive pressure surges
Contamination prevention: Stops dirty or contaminated media from flowing back into clean supply lines or process circuits
System integrity: Maintains pressure in downstream sections of a pipeline when upstream equipment is shut down or fails

Unlike manually operated valves (ball valves, butterfly valves), a non-return valve cannot be left accidentally open – it closes automatically the moment forward flow ceases.

FERGO's non-return valve range (flap-type check valves) covers 3 subcategories spanning wafer, dual plate, and threaded connection types:

Wafer Check Valves (Single Flap – RK100 series) – Inter-flange wafer body for installation between PN10/16/25/40 flanges per EN 1092-1 form B / DIN 2632/2633. Single hinged flap (disc) on a hinge pin. Body: stainless steel 1.4408 or galvanised steel 1.0619; Flap: SS 1.4408/1.4581; Spring: SS 1.4571 (optional return spring); Seat: NBR, EPDM, PTFE, FKM/Viton, or metal. Sizes DN32–DN300; max. 16 bar; temp. up to +200°C (PTFE seat) or +300°C (metal seat). The standard choice for general industrial backflow prevention.
Dual Plate Check Valves (RF200 / RF202 series) – Two spring-loaded half-disc plates on a central shaft, closing simultaneously from the centre outward. Wafer body for installation between PN10/16 flanges per EN 558-1 series 16. RF200: GGG40 ductile iron body, CF8M flaps, SS316 shaft & spring; NBR (max. 80°C) or EPDM (max. 120°C) vulcanised seat; epoxy coating 150 µm RAL 5015. RF202: full SS CF8M body and flaps, SS316 shaft & spring; NBR or EPDM vulcanised. Both: DN50–DN300, PN10/16, max. 16 bar. Fast spring-assisted closure minimises water hammer – ideal for high-flow, large-diameter pipelines.
Threaded Check Valves (RK104 series) – BSP / Rp female thread connection. Body: brass. Seat: NBR, EPDM, or PTFE. Sizes DN10–DN100. The compact, cost-effective solution for smaller installations, instrumentation lines, and utility connections where flanged installation is not required.

For piston-type, nozzle-type, disc (disco), ball, and foot valve check valves, see the separate Check Valves category.

Both types are installed between flanges in wafer construction and prevent backflow automatically, but they differ fundamentally in their closure mechanism and hydraulic behaviour:

Single-flap wafer check valve (RK100):

One full-bore disc hinged on a pin at the top of the body, swinging fully open to one side on forward flow
Closes under gravity (without spring) or spring-assisted return
Without spring: Slower closure – the disc must wait for flow to reverse before gravity pulls it shut; suitable for lower-flow lines where water hammer risk is low; must be installed horizontally with hinge pin horizontal, or vertically with upward flow
With return spring: Faster closure before flow fully reverses; reduces water hammer; allows vertical installation with downward flow
Good for: general industrial backflow prevention, clean and mildly contaminated media, DN32–DN300

Dual plate check valve (RF200 / RF202):

Two spring-loaded half-disc plates on a central shaft, each covering half the bore; they open symmetrically outward and close simultaneously from the centre inward
Spring-assisted closure is intrinsic to the design – the plates close very rapidly as flow decelerates, before any reverse velocity can develop
Key advantage: Dramatically reduced water hammer compared to single-flap designs; the compact, lightweight plates have low inertia and close in milliseconds
Shorter face-to-face than single-flap (per EN 558-1 series 16): saves installation space, especially at large DN
Good for: high-flow pipelines, pump discharge lines where water hammer is a critical concern, DN50–DN300, horizontal and vertical installation

Practical rule: For DN50 and above on pump discharge lines or any high-flow application where water hammer is a risk → prefer dual plate. For smaller sizes, lower flow velocities, or where a return spring on the single-flap is sufficient → wafer single-flap.

The seat elastomer determines which media and temperatures your check valve can handle reliably. FERGO wafer check valves (RK100) are available in five seat options:

NBR (Nitrile Butadiene Rubber) – Temperature range −10°C to +80°C. Good resistance to mineral oils, hydrocarbons, petroleum products, neutral aqueous media, and sewage. The standard seat for water, gas, oils, caustic solutions, and wastewater. Not suitable for hot water above 80°C, steam, or oxidising chemicals.
EPDM (Ethylene Propylene Diene Monomer) – Temperature range −40°C to +120°C. Excellent resistance to hot water, steam, mild acids, alkalis, and ozone. Not compatible with mineral oils, hydrocarbons, or petroleum products. Preferred for drinking water, hot water circuits, chemical applications, and food processing. Standard seat for RF200/RF202 dual plate valves in water service.
PTFE (Polytetrafluoroethylene) – Temperature range −10°C to +200°C. Universal chemical resistance – suitable for the broadest range of aggressive media including acids, alkalis, solvents, and oxidising agents. Lower elastic recovery than elastomers; requires a return spring to ensure reliable sealing. The choice for aggressive chemical media where NBR and EPDM are not compatible.
FKM / FPM (Viton) – Temperature range −10°C to +180°C. Superior resistance to fuels, mineral oils, aromatic and halogenated hydrocarbons, and concentrated acids. More chemical-resistant than NBR at elevated temperatures. Preferred for oil & gas, chemical dosing, and fuel handling applications.
Metal seat – Temperature range −10°C to +300°C. For abrasive media where elastomers would wear rapidly, high-temperature applications beyond elastomer limits (steam, thermal oil), and media containing coarse particles. Bi-directional metal sealing available. A return spring is always required with metal seat construction.

Installation orientation is critical for non-return valves, particularly for single-flap designs, because gravity plays a role in closure:

Wafer single-flap check valve (RK100):

Horizontal installation – Standard orientation; fit with hinge pin axis horizontal (arrow on body pointing in flow direction). Gravity-close models work correctly; the flap swings down under gravity to close. Leave 1–2 pipe diameters of straight pipe on each side to minimise turbulence.
Vertical installation – upward flow: The flap hangs vertically when closed (gravity-aided); works with and without return spring. Flow direction must be upward (arrow pointing up).
Vertical installation – downward flow: Without a return spring, the flap would remain open under its own weight → a return spring is mandatory for downward vertical installation. The spring holds the flap closed when there is no forward flow.

Dual plate check valve (RF200 / RF202):

The spring-loaded dual plate design is inherently suitable for both horizontal and vertical installation in either flow direction, as spring force – not gravity – is the primary closing mechanism
Standard recommendation: install with the hinge shaft axis horizontal in horizontal pipelines
Always ensure the flow direction arrow on the valve body matches the intended flow direction before tightening flange bolts

General installation guidelines:

Provide at least 1–2 pipe diameters of straight pipe upstream and downstream of the valve to ensure fully developed flow and minimise turbulence at the seat
Fit flange gaskets that do not protrude into the bore and interfere with flap movement – use correctly sized gaskets per the valve's flange standard (PN10/16/25/40)
Check that the flap swings freely before tightening the flange bolts to final torque

Water hammer (hydraulic shock) occurs when a sudden change in flow velocity generates a pressure wave that travels through the pipeline. It is most damaging at pump discharge lines when the pump stops – the flow decelerates rapidly, and if the check valve closes slowly (after reverse flow has already developed), the abrupt slam generates destructive pressure spikes that can damage pipes, fittings, and equipment.

The key factor is how quickly the valve closes relative to flow deceleration:

Single-flap without spring (gravity closure): Slowest closure – the flap waits for flow reversal before gravity pulls it shut. Highest water hammer risk on fast-stopping pump systems. Only acceptable where flow velocities are low and pump inertia is high (slow deceleration).
Single-flap with return spring (RK100 + spring): The spring begins closing the flap as forward flow decelerates, before reversal occurs. Significantly reduced water hammer vs. gravity closure. The correct choice for most general industrial pump discharge lines at moderate flow velocities.
Dual plate check valve (RF200 / RF202) with spring: The fastest-closing design in the FERGO range. The two lightweight spring-loaded half-discs have very low inertia and close symmetrically from the centre in milliseconds as flow decelerates – well before any reverse velocity develops. This is the industry-standard solution for water hammer prevention on large-diameter pump discharge lines, high-velocity pipelines, and critical process systems where pressure transients must be minimised.

Recommendation for pump discharge lines (DN50 and above): Always use a dual plate check valve (RF200 or RF202) or at minimum a single-flap valve with return spring. Never use a gravity-only single-flap check valve at pump discharge if water hammer is a concern.

For wafer check valves, the choice of body material determines both corrosion resistance and cost:

Stainless steel 1.4408 / CF8M (AISI 316):

Full corrosion resistance against aggressive media, acids, alkalis, chlorinated water, seawater, and environments where iron contamination is unacceptable
Max. temperature +200°C (PTFE seat), +300°C (metal seat)
Required for: chemical processing, food & beverage, pharmaceuticals, drinking water, marine and offshore applications
Available in all three subcategories: RK100 wafer single-flap, RF202 dual plate SS, and RK104 threaded (brass body for threaded range)

Galvanised steel 1.0619 (RK100 wafer only):

Lower cost option for neutral, non-aggressive aqueous media where full stainless steel is not required
Suitable for: general water service, HVAC, utilities
Not suitable for: corrosive media, food contact, or high-temperature service

Ductile iron GGG40 / EN-GJS-400-15 (RF200 dual plate only):

Robust and economical body material for water, wastewater, and general utility service
CF8M (SS) flaps and SS316 shaft/spring ensure corrosion-resistant wetted internal parts despite the cast iron body
Epoxy-coated exterior (150 µm, RAL 5015 blue) for corrosion protection
Preferred where cost efficiency is important and the medium is water, sewage, or non-corrosive industrial fluid; DN50–DN300, PN10/16

"Non-return valve" and "check valve" are interchangeable terms for the same device – both describe any automatically operating valve that allows flow in one direction only and prevents reverse flow. The terminology varies by region, industry, and application.

Within the broader check valve family, the fundamental distinction is closure element type. FERGO carries two distinct product lines:

This category – Non-Return Valves (flap-type):

Single-flap wafer (RK100): One hinged disc swinging on a pivot pin; full bore when open; gravity or spring closure; wafer inter-flange body; DN32–DN300; ideal for general industrial backflow prevention
Dual plate (RF200/RF202): Two spring-loaded half-discs; fast closure; water hammer reduction; wafer inter-flange; DN50–DN300; ideal for pump discharge lines
Threaded single-flap (RK104): Brass body with BSP thread; DN10–DN100; for smaller installations

Separate category – Check Valves (piston/disc/ball/nozzle types):

Piston (lift) check valves: A piston or guided disc lifts axially off the seat on forward flow and returns under spring force; compact axial construction; good for vertical pipelines; lower flow capacity than flap types; suited for steam, compressed air, and high-pressure applications
Nozzle (axial/silent) check valves: Streamlined disc guided axially in the flow path; very fast spring closure; minimum water hammer; suitable for high-pressure, high-velocity gas and liquid service
Ball check valves: A ball lifts off the seat on forward flow; good for viscous media and slurries; simple construction
Disc (Disco) check valves: Compact, axial spring-loaded disc; short face-to-face; widely used in chemical and process piping
Foot valves: Check valve with strainer installed at the suction end of a pump intake pipe; keeps the suction line primed

Quick selection guide: Flap types (this category) → for large bore, flanged industrial pipelines. Piston/nozzle types (Check Valves category) → for steam, compressed air, high-pressure, or compact installations.

Ball Check Valves: Robust Backflow Protection for Demanding Media

Technical Designs and Materials for Every Application

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Frequently Asked Questions – Non-Return Valves