How to Select an Acid Resistant Solenoid Valve
The selection of an Acid Resistant Solenoid Valve requires more than just choosing the valve which is advertised as corrosion resistant. The first thing to do is to identify the precise fluid which is going to be controlled. Specify the chemical name, concentration, pH, temperature, viscosity and any other additives or contaminants. Then the compatibility with the valve should be verified with the valve supplier.
1. Chemical Compatibility Verification
Valve body, seals, diaphragm, plunger components and other wetted parts must be resistant to the actual fluid. The resistance properties are different for PTFE, fluoropolymer, engineering plastic, stainless steel and elastomer materials. You can not rely on the material resistance to all acids.
2. Calculation of Pressure Requirements
Verify the minimum and maximum inlet and differential pressures. The direct acting valves can be used in the applications with low or even zero differential pressure, while pilot operated valves usually require some pressure difference.
3. Selection of Required Flow Rate
Select the appropriate orifice and flow coefficient to provide the required flow rate. Oversizing the valve leads to poor control and undersizing โ to excessive pressure losses.
4. Selection of Operating Temperature
Specify maximum and minimum media and ambient temperatures. The temperature can have a significant effect on seal performance and chemical compatibility.
5. Normal Valve Position Selection
Select normally closed (NC) or normally open (NO) according to the process conditions and safety philosophy.
6. Verify Electricity Requirements
Verify the coil voltage, AC or DC power, power consumption, connector type and compatibility with the control system. Special electrical interface may be required for PLC controlled systems.
7. Consider Connection Requirements
Verify the type of the thread, flange, tube connection, port size and installation space.
8. Consider Environmental Conditions
In case if the installation is done in outdoor locations, wet, dusty or chemically exposed, verify the required protection class of the coil and enclosure.
Finally, verify all the parameters with the valve manufacturer under the actual operating conditions. One acid concentration may be acceptable for the valve, while the other acid concentration or temperature is not.
Tips to Avoid Common Mistakes Designing Acid Resistant Solenoid Valves
1. Don’t pick materials by their names
“Acid resistant” material may not be resistant to all acids, all concentrations or all temperatures. You always need to verify the compatibility with the actual media.
2. Don’t forget about seal compatibility
Seal may fail before the valve housing. Consider PTFE, FKM, EPDM or other materials depending on chemical and temperature conditions.
3. Don’t choose the wrong valve size
Poor control can be caused by the oversized orifice and excessive pressure loss by the undersized valve. You need to calculate the required flow before sizing the valve.
4. Check Delta P
Pilot operated valves may not work properly with low pressure differential.
5. Think of Chemical Heat Effect
Chemical resistance varies greatly with the temperature. Don’t just size for the normal operating temperature โ size for the maximum process temperature.
6. Solenoid Coil Protection
Electromagnetic coil should be protected from moisture, chemical vapors, overheating and other environmental influences.
7. Failure Position Consideration
Specify normally closed or normally open valve operation in case of power failure.
8. Avoid Dead Zones
The design of the valve and the piping should avoid the zones, where corrosive fluid can collect and destroy the material.
9. Check Installation Direction
Install the valve in accordance with the manufacturer’s requirements. Incorrect installation may lead to improper valve operation.
