TVCCL sorts out the frequently asked questions and answers as follows. TVCCL recommended that client can also read the FAQ before sending the inquiry to get more valve knowledge!!
Cracking Pressure – Refers to the minimum differential upstream pressure between inlet and outlet at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure. Cracking pressure is also known as unseating head (pressure) or opening pressure.Reseal Pressure – Refers to the pressure differential between the inlet and outlet of the valve during the closing process of the check valve, at which there is no visible leak rate. Reseal pressure is also known as sealing pressure, seating head (pressure) or closing pressure.Back Pressure – Refers to the pressure differential between the inlet and outlet of the check valve when the pressure is higher at the outlet of the valve than that at the inlet or a point upstream of the valve.
Check valves are designed in different types in order to fit to different system applications. Dual plate type and single plate check valve are the most common check valves that have been applied in system design. Both valves have the same purpose to prevent backflow of the system.
The following situations may cause loss of valve’s pin, seat and spring. 1. Water hammer is too large When the water hammer is too large, it will squeeze the internal parts of the valve together with the back pressure, causing the valve disc, seat and spring to break.2. Working pressure Excessive or small pressure may damage internal parts.3. The fluid contains corrosive substances When the fluid has corrosive substances, the valve seat rubber will fall off due to the erosion of the metal surface.4. Installation distance is too short Getting too close to pump, easy to produce spoiler, and damaged valve quickly, furthermore shorten the life of the valve. Because the installation distance is insufficient, it will cause turbulence, which will easily cause water hammer. And each installation environment is different (such as temperature, pressure, etc.), these factors will affect the service lifeIf you have the above environmental issues. please tell us. We will configure the right valve for you based on years of professional experience.
Dual plate check valves can be compared to doors, like the door to your office or home. Typically, you open your office door at the start of the day and close it at the end, which is similar to what happens when a pump is cycled on and off. However, if someone stands at your door and constantly cycles it open and closed, what could happen? In most cases, the hinge pins would fail, since they are the weak link in the operation of your door. Check valves face a similar situation. Pins, stems, springs, or other components that are constantly cycled can fail. That is why it is important to properly select check valves for their possible applications. A check valve with a high Cv in a low flow application is doomed from the start. In a short period of time it will fail, no matter what extraneous engineering feats were used to “make it tougher.” Unfortunately, the installed check valve is blamed for the failure, when in reality the culprit was the application. It is always best to review the application and service conditions with the manufacturer before purchasing a check valve to make sure the correct style is selected and avoid replacing a problem with another problem.Excerpt From WaterWorld Magazine Mike Shorts
Regardless of type or style of valve, the longest trouble-free service will come from valves sized for the application, not the line size, whereby the disc is stable against the internal stop in the open position or fully closed. When these conditions are met, no fluttering of the disc will occur. Unfortunately, most check valves are selected in the same way on/off valves are selected: based on line size and the desire for the largest Cv available. This ignores the fact that, unlike on/off valves, the flow conditions determine the internal performance of the check valve since its disc is always in the flow stream.As mentioned earlier, unlike on/off valves, check valve internals are flow sensitive. If there is not enough flow, disc movement occurs inside the valve since the disc is always in the flow path. This results in wear, potential for failure, and a higher pressure drop than calculated.Whenever a metal part rubs against another metal part, wear is a result, which leads to eventual failure of the component. A component failure can result in the valve not performing its function, which in the case of a check valve is to prevent reverse flow. In extreme cases, failure could result in the component or components escaping into the line, causing failure or nonperformance of other valves or equipment in the line.Typically, pressure drop is calculated based on the check valve being 100% open, as with on/off valves. However, if the flow is not sufficient to achieve full opening and the check valve is only partially open, the pressure drop will be greater than calculated since the flow passage is restricted by the disc being in the flow path. In this situation, a large-rated Cv actually becomes detrimental to the check valve (unlike with on/off valves), resulting in fluttering of the disc and eventual failure. Such is not the case with some other valves. With a gate valve, for example, if the valve is fully open, the wedge is out of the flow path and the flow through the valve does not affect the performance of the wedge whether that flow is low, medium, or high.Excerpt From WaterWorld Magazine Mike Shorts
Two of the most common problems with check valves are reverse flow and water hammer. In both situations, a fast-closing valve is desired. Reverse flow can be costly, especially if it occurs at the discharge of a pump and the pump spins backwards. The cost to repair or replace the pump, plus the plant downtime, far exceeds the cost of installing the right check valve in the first place. With water hammer, you need a faster-closing check valve to prevent pressure surges and the resulting shock waves that occur when the disc slams into the seat, sending noise, vibration, and hammering sounds that can rupture pipelines and damage equipment and pipe supports. If the internals are missing or exhibiting wear, two factors may be occurring. First, if the check valve selected does not have enough flow passing through to keep it against its stop, a valve with a lower Cv is needed to prevent the moving/fluttering of the internals. Second, if the check valve is used at the discharge of a reciprocating air or gas compressor, a valve with a damped design or dashpot to handle high-frequency cycling is needed.Sticking can occur when scale or dirt is trapped between the disc and body bore. Leakage can happen from damage to the seat or disc or simple trash in the line. An elastomer is needed to provide zero leakage.Excerpt From WaterWorld Magazine Mike Shorts
We all know that Water has weight. If poured the water directly into the valve, the discs must not stop leaking. In response to specific customer needs, TVCCL has developed a check valve that “No leakage after pouring the water”. As the photos show, the valve body has been yellowed and rusted after using a long time, but the effect of the stop to leak is still good. The discs photo did not see any traces of water infiltration, showing that the quality of TVCCL could use the long-term and without any issues. TVCCL only provides good quality valves and services to clients. If you have any requirements as above, please leave a message or send the email to us.
Under normal conditions of use, TVCCL spring can be operated more than 100,000 times. The test video is as follows
Q.When Dual Plate Check Valves For Stainless Steel Material Is Be Passive Or Active - Formation Of The Passive Layer
The inherent corrosion resistance of stainless steels is derived from alloying the base iron with chromium. BS EN 10088-1 states that a steel must have a minimum of 10.5% (by weight) chromium and a maximum of 1.2% carbon to be classified as 'stainless'.Other alloying elements including nickel, molybdenum, nitrogen, titanium (or niobium) are added to form the various grades. These additions are made to enhance the 'basic' corrosion resistance of the steel but can also usefully modify other properties, such as formability, strength and cryogenic toughness.The corrosion resistance of stainless steel arises from a 'passive', chromium-rich, oxide film that forms naturally on the surface of the steel. Although extremely thin at 1-5 nanometres (i.e. 1-5 x 10-9 metres) thick, this protective film is strongly adherent, and chemically stable (i.e. passive) under conditions which provide sufficient oxygen to the surface. This 'normal' condition is the passive state.The key to the durability of the corrosion resistance of stainless steels is that if the film is damaged it will normally self repair (provided there is sufficient oxygen available). However, under certain conditions, the passive state can be broken down, resulting in corrosive attack.If damaged, the film will normally repair itself. If the film is destroyed the surface is said to be in the active state.
The most common forms of corrosion in stainless steel are: a.Pitting corrosion - The passive layer on stainless steel can be attacked by certain chemical species. The chloride ion Cl- is the most common of these and is found in everyday materials such as salt and bleach. Pitting corrosion is avoided by making sure that stainless steel does not come into prolonged contact with harmful chemicals or by choosing a grade of steel which is more resistant to attack. The pitting corrosion resistance can be assessed using the Pitting Resistance Equivalent Number calculated from the alloy content.b.Crevice corrosion - Stainless steel requires a supply of oxygen to make sure that the passive layer can form on the surface. In very tight crevices, it is not always possible for the oxygen to gain access to the stainless steel surface thereby causing it to be vulnerable to attack. Crevice corrosion is avoided by sealing crevices with a flexible sealant or by using a more corrosion resistant grade.c.General corrosion - Normally, stainless steel does not corrode uniformly as do ordinary carbon and alloy steels. However, with some chemicals, notably acids, the passive layer may be attacked uniformly depending on concentration and temperature and the metal loss is distributed over the entire surface of the steel. Hydrochloric acid and sulphuric acid at some concentrations are particular aggressive towards stainless steel.d.Stress corrosion cracking (SCC) - This is a relatively rare form of corrosion which requires a very specific combination of tensile stress, temperature and corrosive species, often the chloride ion, for it to occur. Typical applications where SCC can occur are hot water tanks and swimming pools. Another form known as sulphide stress corrosion cracking (SSCC) is associated with hydrogen sulphide in oil and gas exploration and production.e.Intergranular corrosion - This is now quite a rare form of corrosion. If the Carbon level in the steel is too high, Chromium can combine with Carbon to form Chromium Carbide. This occurs at temperatures between about 450-850 deg C. This process is also called sensitisation and typically occurs during welding. The Chromium available to form the passive layer is effectively reduced and corrosion can occur. It is avoided by choosing a low carbon grade the so-called 'L' grades or by using a steel with Titanium or Niobium which preferentially combines with Carbon.f.Galvanic corrosion - If two dissimilar metals are in contact with each other and with an electrolyte e.g. water or other solution, it is possible for a galvanic cell to be set up. This is rather like a battery and can accelerate corrosion of the less 'noble' metal. It can avoided by separating the metals with a non-metallic insulator such as rubber.
When the surface of stainless steel pipe appears brown rust (point), people were surprised. The general perception towards stainless steel is that it is a super alloy that never rusts. However, the reality is that stainless steel does rust. The word “stain-less” does not imply free from stain or “stain-impossible”. It simply means that the alloy stains less. This is exactly the case with stainless steel. When compared to other metals and alloys, stainless steel the most resistant to corrosion. Stainless steel is an outstanding material with its high resistance to oxidation (rust) and corrosion in many different environments. Such as 304 steel pipe, in the dry and clean atmosphere, there is absolutely excellent resistance to corrosion, but it moved to the near sea area, used in a fog which has large amount of salt containing, will get rust rapidly. Therefore, there not have any kind of stainless steel, in any environment can be resistant to corrosion and not rust.
1. Water cleaning by degreasing agent, cleaning by Supersonic Machine. 2. Dipping in solvent, cleaning by hot water. 3. Dry blowing by air. 4. Final inspection by white cloth for detecting contamination. 5. Pressure testing and visual inspection.
In a pumped system, the water is forced from a lower level to a higher level by means of a pump. The fluid flows in one direction only when the pump is in operation. When the pump stops, the flow of fluid will reduce until it also stops. Because the overall pipeline will be rising, when the fluid stops, it will then return back down the pipe. To prevent this flow reversal entering into the pump, well or intake, a check valve is installed.In many cases, the rate of fluid reversal is not a cause for concern and standard check valves will perform well. However, in pumped systems where fast flow reversal can occur, the selection of the correct check valve is crucial.If a pump stops and the forward flow reverses back down the line towards the pump before the check valve has fully closed, the flow will force the valve door to slam onto its seat. This scenario can almost instantaneously stop the reverse flow and it is this instantaneous stoppage which results in pipeline water hammer. This can produce loud hammer noises which is not the noise of the valve coming into its seated position but is the stretching of the pipe under these conditions.The consequent pressure wave (surge) can cause considerable damage to the system including pipe cracks, bursts, cavitation and implosion due to vacuum pressures being formed. It is also important to note that these failures may not be due to one single, large surge pressure but by repeated surges which eventually cause fatigue failure of the system.It is important to note that other factors are required to ensure a safe and trouble free system. The correct number, types and sizes of air valves, closing and opening times of isolation valves, flow control valves etc all require to be considered to protect the system from pressure surges.To prevent the occurrence of check valve slam, the valve should close either very quickly to prevent the onset of reverse flow or very slowly once reverse flow has developed. For a check valve to close slowly, this requires additional ancillary equipment such as hydraulic dampers which act to cushion the valve door as it comes into its seated position. However, this slower closure does allow the fluid to pass through the check valve until it closes and consideration must be given to the upstream pump to ensure that it is suitable for reverse spin and flow.
A check valve, non-return valve (NRV) or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Simply put, a check valve allows flow in one direction and automatically prevents back flow (reverse flow) when fluid in the line reverses direction. Ceck valve are one of the few self-automated valves that do not require assistance to open and close. Unlike other valves, they continue to work even if the plant facility loses air, electricity, or the human being that might manually cycle them. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. Check valves are found everywhere, including the home. If you have a sump pump in the basement, a check valve is probably in the discharge line of the pump. Outside the home, they are found in virtually every industry where a pump is located. There are various types of check valves used in a wide variety of applications. Basically, check valve is doing the function of avoiding reverse flow no matter what the type is.
Yes, Our dual plate check valve body and seat is integrated molding. Due to we use mold and professional machine make rubber vulcanizationon the valve seat. If you choose rubber seat check valve, it should back to the factory to do replacing.
Please provide working temperature, media, flow, flow rate, working pressure and other detailed information can be estimated parameters for reference, the use of the environment and the situation we do not know clearly, so the data we gave just for reference, cannot be accurate completely to use.
Absolutely, TVCCL provides retail services, if you need it, you can send us inquiry. We will provide you with preferential prices and best delivery. But there need charge freight if not over a certain amount and price.
WCB/CF8/CF8M/CI/DI/B148 C95800(ALBC3) we usually have stock as above; However, to some special materials, like A8904A/CF3M…etc. We need evaluate if it need MOQ or not.NBR→Usually used in WATER & WASTEWATER TREATMENT. EPDM→Usually used in OIL & GAS. VITON→Usually used in CHEMICAL & PETROCHEMICAL. METAL (Same as Body)→Usually used in HIGH TEMPERATURE ENVIRONMENT, HAVE LEAKAGE.※Rubber seat zero leakage Metal seat leakage permitted values according to standard API598, permitted value is “size*700c.c”/MinOtherwise, we have special type named “__________” Under no pressure environment, no leaking when you pouring water into valve.
Getting too close to pump, easy to produce spoiler, and damaged valve quickly, furthermore shorten the life of the valve. With our years of experience in manufacturing valves, it should be expanded durability if followed our recommendation
we will email our Installation and maintenance instruction for your reference at first transaction.