Introduction of diaphragm valve

The diaphragm valve is a special form of shut-off valve that has the following characteristics compared to other valves:
1. Elastically sealed opening and closing parts ensure no internal leakage;
2. Streamlined flow path, resulting in low pressure loss;
3. No filler, so there is no leakage;
4. The valve body and the cover are separated by the intermediate diaphragm, so that the valve cover, the valve stem and the like above the diaphragm are not eroded by the medium;
5. The diaphragm can be replaced and the maintenance cost is low;
6. The lining material is versatile and can be applied to a wide range of media with good corrosion resistance.
Suitable temperature for the use of the body lining material
Lining material (code)
Operating temperature (°C)
suitable    use    Jie    quality
Hard rubber (NR)
-10~+85
Hydrochloric acid, 30% sulfuric acid, 50% hydrofluoric acid, 80% phosphoric acid, alkali, salt, metal plating solution, sodium hydroxide, potassium hydroxide, neutral salt aqueous solution, 10% sodium hypochlorite, wet chlorine gas, ammonia water, most alcohol Organic acids and aldehydes.
Soft rubber (BR)
-10~+85
Cement, clay, cinder ash, granular fertilizer and solid fluid with strong abrasion, various concentrations of thick and viscous liquid.
Neoprene (CR)
-10~+85
Animal and vegetable oils, lubricants and corrosive muds with a wide range of pH changes.
Butyl rubber (HR)
-10~+120
Organic acids, alkali hydroxides, inorganic salts and inorganic acids, elemental gas alcohols, aldehydes, ethers, ketones, esters, and the like.
Polyvinylidene fluoride plastic
(FEP)
≤ 150
In addition to molten alkali metal, elemental fluorine and aromatic hydrocarbons, hydrochloric acid, sulfuric acid, aqua regia, organic acids, strong oxidants, alternating acid and acid, acid and alkali alternate and various organic solvents.
Polyvinylidene fluoride plastic
(PVDF)
≤ 100
Polytetrafluoroethylene and ethylene copolymer (ETFE)
≤ 120
Fusible PTFE plastic
(PFA)
≤ 180
Polychlorotrifluoroethylene plastic
(PCTFE)
≤ 120
enamel
≤ 100
Do not change the temperature difference
Other low-grade corrosion-resistant media other than hydrofluoric acid, concentrated phosphoric acid and strong alkali
Cast iron unlined
Use temperature according to diaphragm material
Non-corrosive medium
Stainless steel unlined
Generally corrosive medium
Diaphragm material use temperature and applicable media
Diaphragm material (code)
Operating temperature (°C)
suitable     use     Jie     quality
Neoprene (CR)
-10~+85
Animal and vegetable oils, lubricants, and corrosive muds with a wide range of pH changes.
Natural rubber (Q grade)
-10~+100
Inorganic salts, purified water, sewage, inorganic dilute acids.
Butyl rubber (Grade B)
-10~+120
Organic acids, alkali hydroxides, inorganic salts and inorganic acids, elemental gases, alcohols, aldehydes, ethers, ketones, esters, etc.
Ethylene propylene rubber (FPDM)
≤ 120
Demineralized water, 40% boron water, 5% ~ 15% nitric acid and sodium hydroxide.
Butadiene rubber (NBR)
-50~+150
Water, oil, waste gas and pollution treatment waste liquid.
Polyfluoroethylene propylene plastic
(FEP)
-50~+150
In addition to molten alkali metal, elemental fluorine and aromatic hydrocarbons, hydrochloric acid, sulfuric acid, aqua regia, organic acids, strong oxidants, alternating acid and acid, acid and alkali alternate and various organic solvents.
Fusible polytetrafluoroethylene plastic (PFA)
≤ 180
Fluororubber (FPM)
-10~+150
It is more resistant to media corrosion than other rubbers and is suitable for inorganic acids, alkalis, oils, synthetic lubricants and oxygen.
Pressure ---- temperature level
The pressure of the rubber-lined diaphragm valve ----the temperature level is shown in Figure a ;
The pressure of the fluorine-lined plastic diaphragm valve ----the temperature level is shown in Figure b ;
Flow characteristics
The flow characteristics of the diaphragm diaphragm valve are shown in the figure below.
That is , it appears to be linear in characteristics before the 60% opening.
 
Installation and maintenance
1. Before installation, carefully check whether the operating conditions of the pipeline are consistent with the applicable range specified by the valve, and clean the inner cavity to prevent dirt from damaging or damaging the sealing components.
2. Do not apply grease to the surface of the rubber-lined laminated rubber diaphragm to prevent the rubber from swelling and affect the service life of the valve.
3. Do not tie the clue to the lifting valve on the handwheel or valve stem during installation.
4. When operating the valve manually, the auxiliary lever should not be used to prevent damage to the drive or seal parts due to excessive torque.
5. The valve should be stored in a dry and ventilated room. It is strictly prohibited to stack. The passages at both ends of the inventory valve must be sealed, and the opening and closing parts should be in a slightly open state.
Failure and elimination
Possible failure
original         because
Eliminate     except    square    law
Handwheel operation is not flexible
1. Stem change
2. Thread damage
1. Replace the valve stem
2. Trim the thread and lubricate
Valve can not automatically open and close when pneumatic
1. Air supply pressure is too low
2. Spring preload is too large
3. Rubber diaphragm damage
1. Increase the supply pressure
2. Reduce spring preload
3. Replace diaphragm
Leakage at the junction of the valve body and the bonnet
1. Loose connection bolt
2. Valve body lining break
1. Fastening bolt
2. Replace the valve body

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