Did you know that, unlike other types of valves, check valves continue to work if a plant loses electricity, air, manpower, or all of the above? They come in a wide variety of sizes, materials, and end connections, and can be used in countless applications.
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So why is it that they’re often improperly sized or selected? It’s because check valves are only as good as their application. Oftentimes the problems with a check valve are not related to the valve itself, but application and other factors. So when you’re problem solving or replacing a check valve, keep these three common problems in mind:
Water hammer is one of the most common check valve problems. Water hammer is a pressure surge that’s caused when a liquid or gas is forced to stop or change direction suddenly, and often occurs when a valve is suddenly closed at the end of a pipeline system. This can result in both noise and vibration, which can in turn lead to damage and additional maintenance or repair costs.
Water hammer can be prevented, however, by using a faster-closing check valve that stops the pressure surges and shock waves that can damage and rupture equipment. Our silent check valves in particular are known for their effectiveness in preventing and in many cases eliminating water hammer.
Reverse flow is another common check valve problem and can be extremely costly, especially when it occurs at the discharge of a pump, causing the pump to spin backwards.
A fast-closing and tight shut off valve is necessary to prevent this problem, and the right spring-assisted in-line check valve will do just that, eliminating reverse flow.
If there is a lot of valve chatter—opening and closing of the valve repeatedly—chances are it’s due to oversizing. What’s important to remember is that check valves should be sized for the application, and not for the line size. You want the disc to be stable against the internal stop in the open position or fully closed; this will result in no repeated fluttering, and therefore no premature failure.
Keep these common problems in mind, select the right check valve for your application and your check valves will last longer and work more effectively for your applications.
Have questions or want to know more information on Check Valves? Contact DFT today or download our full Check Valve catalog to see what options we offer.
Really im happy to read ur article and have problem i have 3 tilting check valve 350 mm but when pump stop i heard very high noise and its close make vibration in all the line and pump and to know the pump discharge is 300 mm.
Please tell me whay can i do to overcome this problem?
The problem you are experiencing is water hammer, also called hydraulic shock. The pump you are describing is most likely discharging into a vertical pipe run. When the pump is running the water column is moving through the pipe system with no problems. When the pump shuts down the water column reverses direction due to gravity and is now flowing back to the pump. The tilting disc check valve will not react to the pump shutdown, but rather to the reversing of the flow by gravity. The tilting disc then slams against the seat in the valve causing a shock wave to be transmitted through the liquid in the pipe system. Left unresolved this repeated pressure shock will damage other components in your system like gauges and flow meters, leading to even more expensive, on-going repairs. The solution is to replace the tilting disc valve with an axial flow check valve like the DFT model Excalibur. This valve will have the same take out dimension as the tilting disc valve and will be a very easy solution to your water hammer problem. Please contact DFT for the name of your closest DFT distributor: https://industrial.dft-valves.com/contact-dft-dft-inc
Dear sir,
In our case check valve is in steam line. We are experiencing chattering noise in normal operation. So is it due to Oversizing of valve.
Hello Rohan,
Yes, the chattering noise usually indicates being oversized but it may also be due to turbulence. If you would like to discuss further, please contact us at dft@dft-valves.com.
Can I upload a video with the sound I hear?
Hello Bart,
If you would like to talk with someone at DFT about a problem you are experiencing, please contact us at dft@dft-valves.com.
Thank you for your inquiry.
The nozzle on the end of a fire hose is one of the most important pieces of equipment that a firefighter has at their disposal when combating a hostile fire. It’s the business end of what we do.
Understanding the nozzle involves more than knowing if a push or a pull opens the bale and if a left or right twist delivers a straight stream. Here are five nozzle questions whose answers you may not know or have forgotten. Either way, knowing your nozzle gives you an edge over your enemy in a fire attack.
Conventional fog nozzles have a fixed or selectable gpm setting. These settings correspond to a particular discharge orifice, or tip size. In order for a conventional nozzle with a fixed opening to operate at the correct nozzle pressure of 100 psi, the proper gpm flow must be supplied. For example, a selectable gallonage nozzle with settings of 30, 60, 95 and 125 gpm will only deliver those flows of 100 psi of nozzle pressure.
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There are two possible results when the conventional nozzle is not supplied with the rated or selected flow. First, inadequate flow provides a weak, ineffective stream that fails to reach the seat of the fire. Second, too much water flow creates excessive nozzle pressure making the hose line more difficult to handle and potentially jeopardizing the safety of the nozzle crew.
With an automatic nozzle, the discharge orifice continually adjusts depending on the flow to the nozzle. This sets the flow being supplied to the proper nozzle pressure and correct velocity for maximum extinguishing capability.
The automatic nozzle uses a principle very similar to that of a pumper relief valve. A highly dependable spring, connected to the baffle that forms the discharge orifice, is balanced against the water pressure in the nozzle.
The pressure-control spring senses any increase or decrease in pressure within the nozzle. It then moves the baffle in or out to maintain a particular tip size necessary to keep the nozzle pressure at 100 psi. In effect, the nozzle is constantly changing tip size to match the water being supplied at that moment.
Automatic nozzles greatly simplify pump operation. Since automatic nozzles are designed to operate at 100 psi nozzle pressure, this becomes the minimum starting point for any operation.
The basic formula for calculating pump discharge pressure is PDP = NP + TPL — PDP is the pump discharge pressure, NP is the nozzle pressure and TPL is the total pressure loss (that’s hose line friction loss plus apparatus friction loss plus elevation pressure).
With an automatic, the nozzle pressure will remain constant and the formula can be rewritten as: PDP = 100 + TPL. So, for a 200-foot pre-connected 1 3/4-inch hose, what pump pressure will be required to flow 150 gpm? Friction loss in 1 3/4-inch hose for 150 gpm is about 28 psi per 100 feet of hose.
The answer: PDP = 100 + (2 x 28); PDP = 100 + 56; PDP = 156.
To flow 150 gpm in this scenario, a pump discharge pressure of 156 psi is required. The required pump pressure will vary depending on the friction loss produced, the amount of flow desired, and the length and size of the hose lay.
The advantage of using an automatic nozzle is that any flow can be delivered by the pump operator and still be controlled by the nozzle operator. Variable flow, constant nozzle pressure, and nozzleman flow control are three essential elements to successful fire streams and fire attack.
If the eductor manufacturer’s recommendations for inlet pressure, maximum hose length and size are followed, the automatic nozzle will adjust itself automatically to the rating of the eductor. With any eductor system, the nozzle valve must be fully open to prevent excessive back pressure on the eductor, which will prevent foam concentrate pickup.
Certain guidelines, however, must be followed. Foam-making is simply the addition of a proper amount of foam concentrate to water. This solution of foam concentrate and water is then mixed with air (aeration) either at the nozzle with aspirating attachments or as the stream pulls air along with it in a non-aspirating application.
Reducing nozzle pressure does account for some reduction in nozzle reaction. But how much reduction in pressure is required to get a significant reduction in reaction? And while reduced reaction may be a positive aspect, what are the negative aspects of choosing a low-pressure nozzle delivery system?
Those advocating for reducing the fog nozzle pressure typically would reduce the required nozzle pressure downward from 100 psi to 75 psi. If the flow is kept constant, the reaction reduction from a 25 percent cut in nozzle pressure is 13 percent. It works out this way: a 200 gpm stream at 100 psi has 101 pounds of reaction; cutting the nozzle pressure to 75 psi reduces the reaction to 88 pounds.
Nozzle pressure is directly related to the velocity of the stream. For the given example, instead of a stream speeding through the fire’s super-heated gases at 80 mph, it goes through at 60 mph. Which one goes farther? Which splashes more when it hits? Which bores through the wood char to get to deep-seated heat?
Make a comparison to the trend of law enforcement in the United States. As the threat to police officers goes up, are they going to smaller guns with fewer bullets in the clip? Are they taking out the bullets and pouring out half the powder? If they cut out half the powder the gun would kick less, be easier to aim, and it wouldn’t hit as hard. Is that what the police want for their weapons?
Fire departments need to ask if this is really what they want for their primary weapon.
Or consider an example that comes closer to home: how many people wish for a shower with less pressure and how many would think that a shower with less pressure does a better job of getting the soap off?
This article, originally published on Oct. 28, 2015, has been updated.
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