Backflow preventer (C) Daniel Friedman Water System Backflow Preventers & Check Valves

  • CHECK VALVES, WATER SUPPLY - CONTENTS: A guide to choosing, installing, & troubleshooting Backflow Preventers & Other Check valves on water supply systems. We discuss: Backflow Preventers on Water Supply Piping; Backflow Preventer Valves on Heating Systems; Check valves on water supply piping & at pump & well water systems; What Types of Check Valves Should be Used on Well Water Piping Systems? Is it a good idea to use more than one check valve on a pump and well system? Check valves used on building drains, sewage ejector pumps, sump pumps.
  • POST a QUESTION or READ FAQs about locating, using, diagnosing, repairing, or replacing well pump check valves and foot valves.

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Check valves on water supply systems:

This article explains water supply piping check valves used on both municipal water supply piping (usually near the water meter) and on private pump and well water supply systems (usually near the well pump).

We describe various types of check valves used on building plumbing and heating systems. Where do we find the water system check valve (if any) and why are check valves used on pump and well systems?

Types of water supply system & well system check valves, flow control valves, water pressure regulators: gravity operated check valves, spring loaded check valves for wells and water piping: selection, installation, maintenance, repair. How to diagnose a bad or leaky check valve - a cause of lost well pump prime. Causes of well & pump check valve failure - Check valves & air at faucets?

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Water Supply System Backflow Preventers & Check Valves

Article Contents

Backflow Preventers on Water Supply Piping

Definition of backflow preventer

Backflow preventer (C) Daniel FriedmanA "backflow preventer" is a check valve installed on potable water supply piping to prevent possible contamination of the water supply system by backflowing but contaminated water from the building into the outside public water supply mains.

In our photo (left) the blue arrow shows direction of water flow from the building supply mains into other in-building plumbing fixtures & equipment. The green arrow points to the backflow prevention device.

Use Backflow Preventers to Protect Public Water Mains from Individual Home Water Piping Contaminants

Check valves installed at the right location on water system piping are a good idea and are required by national and local plumbing codes in many jurisdictions.

In a home served by public or municipal water from a public water main, the home should have a backflow preventer to make sure that potentially unsanitary water from an individual home's piping never flows backwards into the public water mains.

You will see backflow preventers - special check valves - installed on municipal water supply piping , to prevent possibly unsanitary water from inside a building's piping from back-flowing into and contaminating the municipal water supply system piping during a time of loss of municipal water pressure.

Check Valves on Water Supply Piping

Water piping check valve (C) Daniel FriedmanOn private well water systems we still make use of check valves and backflow preventers, principally to prevent loss of well pump prime and to prevent the back-flow of water out of the pressure tank into the well when the pump is not running.

Above-Ground check valves: check-valves may be built into the well pump or physically separate check valves may be installed above-ground in the well piping (shown below).

In-Well Foot Valves: A check valve mounted in the well at the bottom of well water piping is called a foot valve and is described separately


Here we focus on water supply system check valves found on water supply piping above ground, usually in the building or right at or even part of an above ground water well pump.

Check valves used on well water system piping are used to hold pressure in the system when the pump stops. Check valves on well piping also prevent backspin of the well pump, water hammer and upthrust inside the pump. These problems can damage the well pump. [1]

Photograph of a water system check valve

On a well and pump water supply system a check valve may be installed between the incoming water line from the well and the water pump and pressure tank, such as shown in this photograph of a one line jet pump with a check valve right at the water pump inlet.

You can see the check valve as a bronze assembly at the face of the pump, connected to well piping in this photo. (A similar check valve is visible closer to the foundation wall in a different water pump installation shown in the page top photo.)

You'll notice that this is a one-line jet pump system with the inlet or suction line from the well running horizontally from the face of the pump, and the outlet water line rising vertically off of the pump assembly. The pump's electric motor is at the rear of the assembly. (You can see corrosion and leaks on the water line rising from the pump assembly.)

The water pump check valve helps avoid loss of prime (it keeps water from flowing backwards out of the pump and water tank and back into the well when the pump motor has stopped).

What Types of Check Valves Should be Used on Well Water Piping Systems?

When installing, repairing, or updating well water piping systems, use a spring loaded check valve such as the type illustrated just below. Spring loaded check valves close quickly, prevent water hammer, and protect the pump or impeller assembly from back-flowing; most importantly a properly functioning check valve prevents loss of prime in the well piping system. Lost prime can result in burned-up well pump motors and of course loss of water pressure in the building.

"Drop pipe check valves" are spring loaded check valves that are designed to handle the extra weight of piping installed in deep wells where more than 100 feet of vertical well piping is installed.

Other well piping installation instructions recommend installing a check valve on every 250 feet of vertical well piping.

Do not install swing-type check valves on well piping systems. Swing type check valves permit water to flow backwards through the piping system as the valve closes, risking water hammer problems or even equipment damage. [1]

Water piping check valve (C) Daniel Friedman Water piping check valve (C) Daniel Friedman

Our photos above show a typical brass well piping check valve. A spring-loaded internal valve permits water to flow through the valve only in one direction. The check valve helps assure that the jet pump can suck water out of a shallow well - most water pumps cannot move water if the inside of the pump assembly itself is air bound. Atop some pump assemblies you'll see a removable pipe plug which permits water to be poured into the pump to prime it. (DO NOT pour water into or onto the electric motor itself.)

In summary, a well piping check valve prevents water from siphoning back out of the water tank and water pump and down into the (presumably lower) water well when the pump stops running.

Steel bladderless water pressure tank using a drain-back valve and snifter valve (C) Daniel FriedmanA check valve at this location is a great idea and reduces the risk that a failure of the foot valve down in the well leads to inability of the pump to draw water. The foot valve s located at the bottom of the well piping and intended to accomplish the same thing. This is "cheap insurance" or perhaps the foot valve has already failed (or was omitted) at this installation.

What about when we want water to siphon back out of part of a water supply system, such as when we want to drain water out of well piping exposed to freezing.

A similar check valve found typically at or close to the point at which well or lake water piping enters the base of a steel (bladderlerss) water pressure tank mounts both a pressure gauge and a snifter valve at tappings on the check valve top.

You can see one of these valves in our photo at left (the orange arrow points to the check valve body). This valve is installed at the water tank inlet.

Like the valve shown in our photos above, this check valve adds a 1/4" NPT tapping to accept the mount for a pressure control switch and a 1/8" tapping to accept the snifter valve for sysems whose well pipes are exposed to freezing.

The blue arrow points to a snifter valve and the yellow arrow points to a rusty pipe plug where a 1/4" tapping could have been used to install a water pump pressure control switch.

See SNIFTER & DRAIN BACK VALVES for an example of where these check valves are used.

Pros & Cons of Installing Multiple Check Valves on Wells, Pumps, Water Piping

Question: Can I Install a Second Check Valve Near my (above-ground) Well Pump to Prevent Loss of Prime?

I have a small vacation place in VA. It has a 75' well with 1/2 HP jet pump that works fine. Of course, it has the check valve down in the well that works good but I've always been concerned that it may leak down and lose the prime over the winter months when we are not there.

So, I just leave the power on, although I would prefer to turn it off when winter is approaching.

My question is: could I not install another check valve near the pump inlet as a double protection against loosing my prime IF the power is cut off for a 3-4 month period? BUT, if I DID loose prime for some reason, would not the top check valve have to be removed to allow me to prime the pump? - C.S.

Reply: Multiple Check Valves are Generally Not Recommended

I've found the same problem C.S. - a well and pump system that seemed to be just fine and seemed never to lose prime, until we left power off to the pump for a few days. A leaky foot valve slowly leaked all of the water backwards into the well from the pressure tank and jet pump, losing pump prime in the process.

Most plumbing experts agree that if you are having a problem with a leaky check valve at the pump or in the well, it's best to replace the valve. Here are details and some explanation:

It seems so easy that it is tempting to can add a second check valve if the primary check valve, probably the foot valve in the well seems to be misbehaving.

Some Experts Recommend Multiple Check Valves on Well Piping

The Water Systems Council recommends multiple check valves on well piping in some conditions. Paraphrasing, editing and expanding the WSC advice on using check valves with well pump installations::

Jet pumps often incorporate a check valve in the front of the pump assembly.

More than one check valve should always be used in submersible pump installations. On a submersible well pump installation, if your well water pump does not have a built-in check valve [many submersible pumps do have a check valve], a line check valve should be installed in the discharge pipe within 25 feet of the pump and below the drawdown level of the water inside the well. For deeper well pump settings, a line check valve is recommended every 200 feet. [1]

Problems With Multiple Check Valve Installations on Well Water Piping

But there can be some problems where multiple check valves are installed:

  • Reduced water flow: Adding more check valves will also increase the friction loss or obstruction in the well piping, reducing water flow a bit. If your well pump and water flow were marginal you might notice that effect.
  • Water hammer caused by second check valve: When there is a second check valve (besides the foot valve in the well) above ground at the pump, it is possible that the presence of the second valve will add to or even create water-hammer noise in the building.

    Folks who write about water hammer and check valves argue that because the second valve allows the pump to start against so little resistance that the column of water in the piping between pump and foot valve rises rapidly and "bangs" into the second check valve and pump housing, causing water hammer.

    We have read that this problem on large pump and well systems can actually interfere with proper operation of the pressure control switch by causing the switch to "bounce" between the "open" and "closed" positions.

Bottom line: replace the existing leaky check valve. If the leaky check valve is the foot valve in the well you'll face the more troublesome task of opening the well and pulling up the well line and foot valve. But doing so allows inspection of the well line - you may discover that the problem was not even the foot valve, but a hole in the well piping.

See AIR DISCHARGE at FAUCETS, FIXTURES where this is discussed.

Many plumbing experts advise that unless the check valve is part of a water tank makeup air system, it's best to use just one check valve is needed and just one should be installed in most cases. If the check valve on a jet pump has failed, it makes sense to replace the valve, or if needed, the pump assembly.

You can still go ahead and install the second valve if you want to give it a try - but be prepared to remove it if it causes these problems.

Watch out: some U.S. state plumbing codes (Wisconsin perhaps) may prohibit above-ground check valves on well lines, presumably to reduce the chances of drawing contaminants into the well piping and well.

Some Experts Advise Against Multiple Well Piping Check Valves

Watch out: Other well installers and plumbers do not agree with the Water Systems Council advice cited above. These experts recommend that you do not install a second check valve on submersible well pump systems; rely on the valve that is on the submersible pump.

A second check valve can cause contaminants to be drawn into the piping system, or if the second check valve is inside the well (on the vertical well pipe but above the pump), as in our discussion above it may cause water hammer problems in the system. If the check valve on a submersible pump has failed, you should pull the pump and replace that valve.

Where Multiple Check Valves Are Recommended on Well Piping Systems

You may need to install a check valve on the vertical well piping at a rate of one for every 250 feet of vertical rise in the well bore. We mentioned earlier in this article series that

"Drop pipe check valves" are spring loaded check valves that are designed to handle the extra weight of piping installed in deep wells where more than 100 feet of vertical well piping is installed.

Other well piping installation instructions recommend installing a check valve on every 250 feet of vertical well piping.

Check valve research of interest for water supply & well piping systems

  • Pandula, Zoltán, and Gábor Halász. "Dynamic model for simulation of check valves in pipe systems." Mechanical Engineering 46, no. 2 (2002): 91-100.
  • Thorley, A. R. D. "Check valve behavior under transient flow conditions: a state-of-the-art review." Journal of Fluids Engineering 111, no. 2 (1989): 178-183.

Short Cycling of the Water Pump Reduces Check Valve Life

Note: well pump "short cycling" or rapidly turning on and off increases check valve wear and so shortens their life. See our article on well pump short cycling. And variable speed pumping systems (Franklin Sub Drive/Mono-Drive) that cycle the pump on and off very rapidly are still harder on both the pump and the check valve.


Heating System Backflow Preventer Valves Protect Public Water Mains / Private Water Piping from Heating System Water Contaminants

Backflow preventer (C) Daniel Friedman

Because a building potable water supply piping cold water line is used to deliver water to hydronic or steam heating boilers, we need to prevent heating system water from back-contaminating the building water supply piping.

At a hot water heating system a backflow preventer is installed to keep hot, high pressure water in the hydronic heating system from flowing backwards through a boiler water feed line into the building water supply - a sanitation concern.

On heating systems the backflow preventer may be built into the automatic water feed valve

and/or a separate dedicated check valve
BACKFLOW PREVENTER VALVE, HEATING SYS - such as the one in our photo (left) may be installed..

In our heating system backflow preventer photo (green arrow, above) The blue arrow shows the direction of water flow into the water feeder and onwards into the heating boiler.

Research on the Use of Check Valves on Heating Systems

  • Charoensawan, Piyanun, Sameer Khandekar, Manfred Groll, and Pradit Terdtoon. "Closed loop pulsating heat pipes: Part A: parametric experimental investigations." Applied Thermal Engineering 23, no. 16 (2003): 2009-2020.
  • Meena, P., S. Rittidech, and N. Poomsa-Ad. "Closed-loop oscillating heat-pipe with check valves (CLOHP/CVs) air-preheater for reducing relative humidity in drying systems." Applied Energy 84, no. 4 (2007): 363-373.
  • Pandula, Zoltán, and Gábor Halász. "Dynamic model for simulation of check valves in pipe systems." Mechanical Engineering 46, no. 2 (2002): 91-100.
  • Rafferty, Kevin. "Design aspects of commercial open-loop heat pump systems." Geo-Heat Center Quarterly Bulletin 22 (2001): 16-24.
  • Rittidech, S., N. Pipatpaiboon, and S. Thongdaeng. "Thermal performance of horizontal closed-loop oscillating heat-pipe with check valves." Journal of mechanical science and technology 24, no. 2 (2010): 545-550.

Other Applications of Check Valves on Building Plumbing & Piping

Check valves on sump pumps: Check valves are used in other plumbing applications as well, such as on sump pump drain lines to prevent back-flow of water from the sump pump exit piping into the sump pit when the sump pump turns off.

Check valves on sewage ejector pumps: check valves on sewage pumps are used to prevent backflow of sewage into the building piping or sewage pumping chamber from a sewer main (or septic tank) located higher than the building.
See SEWAGE PUMPS for details.

Check valves on building drains are installed to prevent sewage backups into buildings. Check valves are also installed on drain piping such as on some sewer lines (where sewer backups are likely) and on sump pumps discussed

Research on check valves used on sewage and other drain systems

  • Dickenson, T. Christopher. Valves, Piping, and Pipelines Handbook. Elsevier, 1999.
  • Lee, Joseph HW, David L. Wilkinson, and Ian R. Wood. "On the head-discharge relation of a" duckbill" elastomer check valve." Journal of Hydraulic Research 39, no. 6 (2001): 619-627.
  • Lee, Joseph HW, Jaydeep Karandikar, and Peter R. Horton. "Hydraulics of “duckbill” elastomer check valves." Journal of Hydraulic Engineering 124, no. 4 (1998): 394-405.

Description of Types of Water Flow Control Valves & Water Pressure Regulators

Question: What's a flow control valve and why are they used on water well piping systems

I've heard that some well water systems need a flow control valve. What is a flow control valve and why would one be used on well piping? - Anon

Reply: Description of the water flow control valves & types of water pressure regulators & their applications

According to the Water Systems Council [paraphrased, edited, and expanded-Ed.]

Flow-control valves are used on well water piping systems in order to reduce or limit the amount of pump capacity - that is, to control the rate or flow of water delivered by the well pump. Flow control valves are installed mainly to prevent an overload on the well pump motor (thus limiting the current or amps drawn by the well pump) and also to control the degree of upthrust pressure on the water pump.

When well flow rate and well pump flow rate capacity conditions could allow the water pump to deliver too much capacity, a flow control valve may be installed to restrict the water flow to an adequate amount while preventing it from being excessive.

For example, a flow rate valve may be installed on a well system at which the well flow rate is rather poor. This prevents the pump from getting "ahead" of the in-flow rate of water into the well, thus protecting the well pump from running dry and becoming damaged.

Flow-control valves of this type are also installed on showers or other water-using appliances to limit the gallons-per-minute flow to these outlets. A set flow rate to equipment such as irrigation systems can also be maintained with flow-control valves. [1]

Flow control of municipal water supply into a building is provided by a water pressure regulator, a similar device that drops high incoming pressure at the water main down to (typically) 70 psi or less in order to protect the building piping from leaks caused by excessive water pressure. Details are

Flow-control of domestic hot water is also often limited by a flow control valve or tempering valve where the hot water source is of limited flow rate capacity, such as at tankless coils and at demand or tankless water heaters. In that case we limit the flow rate of cold water through the hot water heating device to a rate slow enough that the water will be adequately heated.


Water feeders & pressure regulators for heating equipment: hot water heating boilers & steam boilers are also protected from water loss by several types of automatic water feed valves that add water to the heating system when needed.

Hot water heating system automatic water feeder/pressure reducing valves at factory setting typically will feed water into a Hydronic heating boiler up to a 12 psi cutoff (or higher if necessary) if the system pressure when cold falls below 12 psi. Details are

and at WATER FEEDER VALVE, STEAM or select a topic from the More Reading links shown below.



Continue reading at WATER PRESSURE REDUCER / REGULATOR or select a topic from the More Reading links shown below.

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CHECK VALVES, WATER SUPPLY at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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