In chemical piping systems, selecting a valve that is compatible with the properties of the medium is an important factor in ensuring stable operation and minimizing the risk of corrosion. In particular, when a system uses acid, alkali, or corrosive liquids and gases, the materials used to manufacture the valve body, diaphragm, and components in contact with the medium need to be carefully considered.

The COVNA VALVE HKFP21 Series is an anti-corrosion solenoid valve designed with an isolated diaphragm construction and a PTFE valve body, intended for applications involving corrosive media. According to the provided technical information, the valve can be used for corrosive fluid and gas, acid, alkali, with port size options from 1/8″ to 1/2″, orifice sizes of 3 mm and 6 mm, and multiple AC/DC voltage options.

1. Overview of the COVNA VALVE HKFP21 Anti-Corrosion Solenoid Valve

The COVNA VALVE HKFP21 Series is a solenoid valve using an isolated diaphragm construction to control the opening and closing of the medium flow. A key feature of the valve is its PTFE body and PTFE seal, making the product configuration suitable for applications involving corrosive media.

According to the technical documentation, the applicable media include:

• Corrosive liquids.
• Corrosive gases.
• Acid.
• Alkali.
• Other media compatible with the PTFE valve material.

The valve is designed in a NC – Normally Closed configuration, meaning that the valve remains closed when the coil is de-energized and opens when the coil is energized according to the operating conditions of the product.

The COVNA HKFP21 is available with the following port sizes:

1/8″, 1/4″, 3/8″ and 1/2″.

The available orifice sizes include:

3 mm and 6 mm.

The valve series also provides multiple voltage options, including:

• DC 12V
• DC 24V
• AC 24V
• AC 120V
• AC 240V / 60Hz
• AC 110V
• AC 220V / 50Hz

This allows the valve to be selected according to the available power supply of the system.

2. Key Features of the COVNA HKFP21 Solenoid Valve

2.1. Corrosion-resistant PTFE valve body

The valve body of the HKFP21 is manufactured from PTFE.

This is an important characteristic of the valve when it is used in corrosive environments. Instead of using a metal body as the primary material in contact with the medium, the PTFE configuration is intended for applications involving acid, alkali, and corrosive media that are confirmed to be compatible.

However, actual application suitability needs to be verified based on the type of medium, concentration, temperature, and specific operating conditions.

2.2. Isolated diaphragm construction

The HKFP21 uses an isolated diaphragm construction.

The diaphragm construction plays an important role in separating the operating mechanism from the medium. This is suitable for applications where the medium is corrosive and unnecessary contact between the medium and internal components needs to be minimized.

2.3. PTFE seal

The valve seal is specified as PTFE.

The combination of:

PTFE Body + PTFE Seal

provides a material configuration intended for the corrosive-media applications of the HKFP21 Series.

2.4. Multiple voltage options

The HKFP21 provides AC and DC voltage options, including:

DC-12V, DC-24V, AC-24V, AC-120V, AC-240V/60Hz, AC-110V and AC-220V/50Hz.

This allows the user to select a coil compatible with the actual control power supply.

2.5. 100% ED coil operation

The documentation provides two coil series:

• Y82B
• YD1B

Both are specified with a 100% ED (100% duty cycle) operating mode, suitable for continuous coil energization when operated within the technical limits of the product.

3. Media and Application Range

The HKFP21 is designed for applications involving corrosive fluid and gas, acid, alkali. Therefore, the valve can be considered for systems requiring automatic control of corrosive media.

3.1. Acid

In systems using acid, valve material is one of the first factors that needs to be checked.

The PTFE body and PTFE seal of the HKFP21 make the product suitable for consideration in this type of application. However, it should not be assumed that the valve is compatible with every type of acid.

The following parameters need to be determined:

• Type of acid.
• Concentration.
• Temperature.
• Pressure.
• Liquid or gas state.

These parameters should then be compared with the material compatibility of the valve before selection.

3.2. Alkali

The HKFP21 documentation also specifies alkali applications.

Similar to acid service, valve selection should be based on the actual type and concentration of the alkali rather than simply the general chemical category.

3.3. Corrosive liquids and gases

The valve can be considered for corrosive fluids and gases when the medium falls within the compatibility range of PTFE and the other components in contact with the medium.

3.4. Chemical systems

In chemical handling and dosing systems, a solenoid valve can perform the function of automatically opening and closing the chemical flow according to control signals.

Potential installation points include:

• Chemical supply lines.
• Dosing lines.
• Small-diameter chemical pipelines.
• Acid/alkali supply systems.
• Equipment requiring automatic chemical flow control.

Final selection should be based on the actual system parameters.

4. Technical Specifications of the HKFP21 Solenoid Valve

The following specifications are summarized from the technical information provided:

Specification	HKFP21 Series
Series	HKFP21
Valve type	Solenoid Valve
Construction	Isolated Diaphragm
Operating state	NC – Normally Closed
Medium	Corrosive fluid and gas, Acid, Alkali
Body material	PTFE
Seal	PTFE
PTFE Seal Temperature	-20°C to 180°C
Port size	1/8″, 1/4″, 3/8″, 1/2″
Port thread	BSPP, BSPT, NPT, Flange
Orifice	3 mm, 6 mm
Voltage	DC12V, DC24V, AC24V, AC120V, AC240V/60Hz, AC110V, AC220V/50Hz
Tolerance	±10%
Coil	Y82B, YD1B
Duty cycle	100% ED

According to the provided information, different HKFP21 configurations are specified with different pressure ratings depending on the orifice/configuration. Therefore, when selecting the product, the specific model and corresponding technical table should be checked rather than applying one common pressure rating to the entire HKFP21 Series.

5. Valve Construction and Materials

One of the important features of the HKFP21 is the material selection of each component, which is intended to suit the operating environment.

5.1. Body – PTFE

The body is made of PTFE.

The valve body forms the medium flow path and is one of the most important components to consider regarding corrosion resistance.

5.2. Seal – PTFE

The seal is made of PTFE.

According to the technical information, the PTFE seal temperature range is:

-20°C to 180°C.

This limit needs to be considered together with the actual medium temperature and the other limits of the complete valve.

5.3. Armature Tube – Stainless Steel 304

The armature tube is made of Stainless Steel 304.

This component belongs to the solenoid operating mechanism and is not the main flow path body of the valve.

5.4. Plunger – Stainless Steel 430F

The plunger is made of Stainless Steel 430F and performs the movement within the solenoid mechanism when the coil is energized.

5.5. Stop – SS403F

The stop is made of SS403F.

5.6. Springs – Stainless Steel 304

The springs are made of Stainless Steel 304, supporting the operating mechanism of the valve.

5.7. Shading Rings – Stainless Steel 304

The shading rings are made of Stainless Steel 304.

Overall, the HKFP21 material configuration consists of:

PTFE Body + PTFE Seal + Stainless Steel 304 + Stainless Steel 430F + SS403F.

This material configuration should be checked against the actual medium before the valve is installed in the system.

6. Guide to Selecting the HKFP21 Solenoid Valve

To select the correct COVNA HKFP21 solenoid valve, several parameters need to be determined rather than selecting the valve based only on pipe size.

6.1. Select the port size

The HKFP21 is available with:

• 1/8″
• 1/4″
• 3/8″
• 1/2″

The port size should match the pipeline connection and the required flow rate of the system.

6.2. Select the orifice

The documentation provides two orifice options:

• 3 mm
• 6 mm

The orifice directly affects the flow capacity of the valve.

Therefore, the required flow rate should be determined before selecting the orifice.

6.3. Select the connection type

The HKFP21 is available with:

• BSPP
• BSPT
• NPT
• Flange

The exact connection standard of the pipeline should be confirmed before ordering.

6.4. Select the voltage

The power supply must be compatible with the coil.

The available options shown in the documentation include:

DC12V / DC24V / AC24V / AC110V / AC120V / AC220V / AC240V.

The frequency should also be considered:

• AC110V, AC220V: 50 Hz
• AC120V, AC240V: 60 Hz

6.5. Check the pressure

Operating pressure is a mandatory parameter that must be confirmed before valve selection.

According to the documentation, the HKFP21 has different pressure ratings depending on the configuration. Therefore, the exact model, orifice and coil should be identified before checking the allowable pressure.

7. Installation and Operation Instructions

Correct installation has a direct impact on the operating performance of the solenoid valve.

7.1. Check the medium before installation

The valve should only be used with clean liquids or gases that are compatible with the technical specifications.

The documentation recommends installing a 500 µm filter upstream of the solenoid valve to limit dirt or foreign particles from entering the valve.

7.2. Identify the correct flow direction

If an arrow is marked on the valve body, the valve must be installed according to the indicated flow direction.

Incorrect installation may affect valve operation.

7.3. Secure the pipeline

The pipes on both sides of the valve must be securely supported.

When tightening the connection, use suitable wrenches for both the valve and the pipe to minimize unnecessary forces acting on the valve body.

Do not apply force to the coil or armature when tightening the connection.

7.4. Prevent sealing material from entering the valve

When using thread sealing material, prevent the material from entering the inside of the valve.

Such material may block the orifice or interfere with the valve operating mechanism.

7.5. Recommended installation position

The documentation recommends installing the valve in a vertical position with the coil facing upward.

This installation position helps reduce the possibility of debris accumulating in the solenoid valve.

7.6. Do not exceed the technical limits

The following limits must not be exceeded:

• Pressure.
• Temperature.
• Voltage.

The medium must also be compatible with the valve materials.

8. Common Faults and Troubleshooting

During operation, certain faults may occur due to the power supply, pressure, foreign particles, or internal mechanical components.

8.1. Valve fails to operate

If the valve does not operate, check the following:

1. Check the power supply

Use a voltmeter to check the voltage supplied to the coil.

The voltage must correspond to the rating shown on the nameplate.

2. Check the coil

Use an ohmmeter to check whether the coil is open-circuited or short-circuited.

3. Check the pressure

Make sure that the actual pressure is within the allowable range of the specific model.

8.2. Valve is sluggish or inoperative although electrical supply and pressure are normal

If the electrical supply and pressure are both normal:

• Disassemble the valve for inspection.
• Remove foreign matter and contamination.
• Check whether the plunger can move freely or is binding.
• Check the diaphragm.
• Check the bleed hole or pilot orifice.
• Check the springs.

If the diaphragm is torn, it must be replaced.

If a spring is broken, the damaged component must be replaced.

8.3. External leakage

If leakage occurs at the sleeve flange or at the joint between the body and cover, check:

• Sleeve tightening.
• Cover screws.
• Sealing surfaces.
• O-rings.

If leakage persists, the diaphragm assembly, flange O-ring, or components with damaged sealing surfaces may need to be replaced.

8.4. Internal leakage

When internal leakage occurs:

1. Disassemble the valve.
2. Remove foreign matter.
3. Clean the components with a mild soap and water solution.
4. Check the diaphragm sealing surface.
5. Check the orifice.
6. Check the plunger return spring.

If damaged components are found, they should be repaired or replaced as appropriate.

8.5. Chatter or buzz sound when energized

When abnormal chatter or buzz occurs:

1. Disconnect power from the coil.
2. Inspect the plunger.
3. Inspect the sleeve.
4. Check for excessive wear.
5. Check for contamination or foreign particles.

Contamination or excessive wear may affect the movement of the solenoid mechanism.

9. COVNA VALVE HKFP21 – A Solution for Controlling Corrosive Media

For systems requiring automatic opening and closing of corrosive media, selecting suitable valve materials is one of the important considerations.

The COVNA VALVE HKFP21 Series is designed with:

PTFE Body + PTFE Seal + Isolated Diaphragm Construction

together with solenoid mechanism components manufactured from materials such as SS304, SS430F and SS403F.

The valve series provides port sizes from 1/8″ to 1/2″, orifice sizes of 3–6 mm, multiple connection types, and various AC/DC voltage configurations.

In particular, the isolated diaphragm construction makes the HKFP21 suitable for consideration in applications requiring control of corrosive media such as acid, alkali, corrosive fluid and corrosive gas.

However, compatibility should not be determined solely by the fact that the valve uses PTFE. The user needs to verify the type of medium, concentration, temperature, pressure, flow rate, and operating conditions to determine the appropriate model and configuration.

10. Conclusion

The COVNA VALVE HKFP21 Series Anti-Corrosion Solenoid Valve is designed for applications requiring automatic opening and closing of fluid flow, particularly systems using corrosive liquids and gases, acid and alkali.

A key feature of the product is its PTFE valve body, PTFE seal, and isolated diaphragm construction, combined with a solenoid mechanism using materials such as Stainless Steel 304, Stainless Steel 430F and SS403F.

The HKFP21 provides multiple options for:

• Port sizes 1/8″–1/2″.
• Orifice sizes 3 mm and 6 mm.
• Connections BSPP, BSPT, NPT or Flange.
• Voltages DC12V, DC24V, AC24V, AC110V, AC120V, AC220V and AC240V depending on the configuration.
• Coils Y82B and YD1B.
• PTFE seal temperature range specified in the documentation from -20°C to 180°C.

During valve selection and installation, particular attention should be paid to medium compatibility with the materials, pressure, temperature, voltage, and operating conditions. Installing a filter upstream of the valve, ensuring the correct flow direction, and performing regular inspections can also help minimize problems caused by contamination or unsuitable operating conditions.

The COVNA VALVE HKFP21 can be considered for chemical treatment systems, acid/alkali pipelines, and other industrial applications requiring automatic control of corrosive media, provided that the model and configuration are properly selected according to the actual system requirements.