# How Does a Solenoid Valve Work? A Complete Technical Guide
When it comes to precise fluid control in industrial applications, understanding **how solenoid valves work** is essential for engineers, technicians, and procurement professionals. At COVNA GROUP CO., LTD, we've manufactured industrial valves since 2008, supplying over 5,000 valve solutions globally. This comprehensive guide explains the working principles, components, applications, and selection criteria for solenoid valves.
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## What is a Solenoid Valve?
A **solenoid valve** is an electromechanically operated valve that controls the flow of liquids or gases through a pipe or tube. Unlike manual valves that require physical turning or pressing, solenoid valves operate automatically when an electrical current is applied, making them ideal for automation systems and remote control applications.
### Key Characteristics of Solenoid Valves:
- **Electromechanical operation**: Uses electromagnetic force to actuate the valve
- **Fast response time**: Can open or close in milliseconds
- **Remote controllability**: Can be operated from a distance via electrical signals
- **Automation compatibility**: Integrates seamlessly with PLC and control systems
- **Repeatable precision**: Provides consistent operation over millions of cycles
---
## The Basic Working Principle of Solenoid Valves
Understanding **how solenoid valves work** requires examining the electromagnetic principle that powers these devices. The operation follows a straightforward yet elegant sequence:
### Step-by-Step Working Process:
**1. Rest State (De-energized)**
- When no electrical current flows through the solenoid coil, the valve remains in its default position
- In a **normally closed (NC)** valve, the plunger seals the orifice, preventing flow
- In a **normally open (NO)** valve, the flow path remains open
**2. Electromagnetic Activation**
- When voltage is applied to the coil, electrical current generates a magnetic field
- The magnetic field strength follows the formula: **B = μ₀ × n × I** where:
- B = magnetic flux density
- μ₀ = permeability of free space
- n = number of coil turns per unit length
- I = current through the coil
**3. Plunger Movement**
- The magnetic field attracts the ferromagnetic plunger (armature)
- The plunger moves against the spring force, overcoming the mechanical resistance
- Movement distance typically ranges from 2-15mm depending on valve size
**4. Valve State Change**
- For **normally closed valves**: Plunger lifts off the orifice, opening the flow path
- For **normally open valves**: Plunger seals against the orifice, closing the flow path
- Flow is now either permitted (NC) or blocked (NO)
**5. De-energization and Return**
- When voltage is removed, the magnetic field collapses
- The return spring pushes the plunger back to its original position
- The valve returns to its default state (NC closed, NO open)
---
## Key Components of a Solenoid Valve
Understanding the individual components helps explain **how solenoid valves work** and aids in troubleshooting. Here are the essential parts:
### 1. Solenoid Coil
- **Function**: Generates the electromagnetic field when energized
- **Construction**: Copper wire wound around a bobbin, typically 500-5000 turns
- **Voltage ratings**: Common options include 12V DC, 24V DC, 24V AC, 110V AC, 220V AC
- **Power consumption**: Typically 5-30 watts depending on size
- **Insulation class**: Usually Class F (155°C) or Class H (180°C)
### 2. Plunger (Armature)
- **Function**: Moves within the magnetic field to open/close the valve
- **Material**: Soft iron or stainless steel with high magnetic permeability
- **Design**: Precision-machined to minimize air gap and maximize magnetic flux
- **Coating**: Often nickel-plated or coated to prevent corrosion
### 3. Valve Body
- **Function**: Contains the fluid path and houses internal components
- **Materials**:
- Brass (most common for general purpose)
- Stainless steel 304/316 (corrosion resistant, food grade)
- PVC/PTFE (chemical resistant)
- Aluminum (lightweight)
- **Connections**: Threaded (BSP, NPT), flanged, or compression fittings
- **Pressure ratings**: From vacuum to 100+ bar depending on design
### 4. Seal and Seat
- **Function**: Creates a leak-tight closure when the valve is closed
- **Seat materials**: Brass, stainless steel, or PTFE depending on application
- **Seal materials**:
- NBR/Nitrile (general purpose, oil resistant)
- EPDM (hot water, steam, acids)
- Viton/FKM (chemicals, high temperature)
- PTFE (corrosive chemicals, food grade)
- Silicone (food, medical, low temperature)
### 5. Spring
- **Function**: Returns the plunger to its default position when de-energized
- **Material**: Stainless steel or music wire
- **Design**: Compression spring sized to overcome friction and gravity
- **Preload**: Engineered to ensure reliable return without excessive force
### 6. Electrical Connection
- **Function**: Provides power to the solenoid coil
- **Types**:
- DIN 43650A connector (most common industrial standard)
- Flying leads with conduit
- Junction box
- Terminal block
- **Protection**: IP65/IP67 ratings for harsh environments
- **Features**: LED indicators, surge suppression, polarity protection
---
## Types of Solenoid Valves and Their Applications
Understanding the different types of solenoid valves helps in selecting the right valve for your application. Here's a comprehensive breakdown:
### By Operating Configuration
**1. 2-Way Solenoid Valves**
- **Configuration**: One inlet, one outlet
- **Function**: Simple on/off control of flow
- **Applications**: General fluid control, water systems, air systems
- **Common sizes**: 1/8" to 3" ports
- **Example**: COVNA 2W Series Brass Solenoid Valve
**2. 3-Way Solenoid Valves**
- **Configuration**: One inlet, two outlets (or two inlets, one outlet)
- **Function**: Diverting or mixing applications
- **Applications**: Cylinder control, actuator operation, diverting flow
- **Operation types**:
- Universal: Can function as normally closed or normally open
- Directional: Specific flow paths for different applications
- **Example**: COVNA 3V Series 3-Way Solenoid Valve
**3. 4-Way and 5-Way Solenoid Valves**
- **Configuration**: Multiple inlet/outlet combinations
- **Function**: Complex directional control
- **Applications**: Double-acting cylinders, complex pneumatic circuits
- **Common in**: Pneumatic automation systems
### By Default Position
**1. Normally Closed (NC) Solenoid Valves**
- **Default state**: Closed, no flow when de-energized
- **Activated state**: Opens when energized
- **Applications**: Safety-critical systems, emergency shut-off, process control
- **Advantages**: Fail-safe operation (closes on power loss)
- **Common uses**: Fuel systems, gas controls, chemical dosing
**2. Normally Open (NO) Solenoid Valves**
- **Default state**: Open, allows flow when de-energized
- **Activated state**: Closes when energized
- **Applications**: Cooling systems, venting applications
- **Advantages**: Allows flow during power failures
- **Common uses**: Cooling water, ventilation systems
**3. Universal (Bi-stable/Latching) Solenoid Valves**
- **Operation**: Stays in last position without continuous power
- **Activation**: Pulse of power changes state
- **Advantages**: Energy efficient, battery-operated systems
- **Applications**: Remote locations, solar-powered systems
### By Connection Type
**1. Threaded Solenoid Valves**
- **Types**: BSP (G), NPT, BSPT
- **Sizes**: 1/8" to 3" (DN4 to DN80)
- **Applications**: General industrial, mobile equipment
- **Advantages**: Easy installation, widely available
- **Materials**: Brass, stainless steel, plastic
**2. Flanged Solenoid Valves**
- **Standards**: ANSI, DIN, JIS
- **Sizes**: 1/2" to 24" and larger
- **Pressure ratings**: PN10, PN16, PN25, PN40, Class 150, 300
- **Applications**: Large flow applications, high-pressure systems
- **Materials**: Cast iron, carbon steel, stainless steel
**3. Compression Fitting Solenoid Valves**
- **Types**: Tube fittings, quick-connect
- **Sizes**: 4mm to 22mm tubing
- **Applications**: Pneumatic systems, instrumentation
- **Advantages**: Easy assembly, reusable
**4. Manifold Mount Solenoid Valves**
- **Configuration**: Multiple valves on common manifold
- **Applications**: Complex pneumatic circuits
- **Advantages**: Compact design, common supply/exhaust
- **Common in**: Automation machinery, packaging equipment
---
## Electrical Specifications and Power Requirements
Selecting the correct electrical specifications is crucial for proper valve operation and system compatibility.
### Voltage Options
**DC Voltage (Direct Current):**
| Voltage | Common Applications | Advantages |
|---------|-------------------|------------|
| 6V DC | Battery-powered, automotive | Low power, portable |
| 12V DC | Automotive, marine, solar | Standard vehicle systems |
| 24V DC | Industrial automation, PLCs | Safety extra-low voltage |
| 48V DC | Telecom, data centers | Reduced current for long runs |
**AC Voltage (Alternating Current):**
| Voltage | Frequency | Common Applications |
|---------|-----------|-------------------|
| 24V AC | 50/60Hz | HVAC, refrigeration controls |
| 110-120V AC | 60Hz | North American residential/commercial |
| 220-240V AC | 50Hz | European, Asian, international |
| 380-415V AC | 50Hz | Industrial three-phase systems |
### Power Consumption
**Understanding Power Ratings:**
| Valve Size | Typical Power (DC) | Typical Power (AC) | Inrush Current (AC) |
|------------|-------------------|-------------------|-------------------|
| 1/8" - 1/4" | 4-8W | 6-10VA | 10-20VA |
| 3/8" - 1/2" | 8-15W | 10-20VA | 20-40VA |
| 3/4" - 1" | 15-25W | 20-40VA | 40-80VA |
| 1"+ | 25-50W+ | 40-80VA+ | 80-150VA+ |
**Important Notes:**
- DC valves draw continuous power when energized
- AC valves have high inrush current when first energized, then settle to holding current
- Power consumption affects heat generation and energy costs
### Coil Specifications
**Insulation Classes:**
| Class | Max Temperature | Typical Applications |
|-------|-----------------|-------------------|
| Class A | 105°C | Standard industrial |
| Class E | 120°C | Elevated temperature |
| Class B | 130°C | Hot environments |
| Class F | 155°C | High temperature (most common) |
| Class H | 180°C | Extreme temperature |
**Enclosure Types:**
| Type | Protection | IP Rating | Applications |
|------|-----------|-----------|--------------|
| Open | No protection | IP00 | Clean indoor |
| Conduit | Threaded conduit | IP54 | General industrial |
| DIN 43650A | Standard connector | IP65 | Most common industrial |
| DIN 43650B | Larger connector | IP65 | High current |
| Terminal box | Screw terminals | IP65/IP67 | Harsh environments |
| Explosion-proof | Flameproof | Ex d | Hazardous areas |
**Special Features:**
- **LED indicator**: Visual status indication
- **Surge suppression**: Protection against voltage spikes
- **Polarity protection**: Prevents damage from reverse connection (DC)
- **Rectifier**: Converts AC to DC for coil (AC coils)
- **Bipolar**: Can work with either polarity (DC)
### Selection Guidelines
**Step-by-Step Selection Process:**
1. **Determine Voltage**: Match to your control system
- PLC outputs: Usually 24V DC
- Relay control: Match relay coil voltage
- Direct control: Available supply voltage
2. **Select Power Type**: AC or DC
- DC preferred for: Electronic control, battery systems, safety circuits
- AC preferred for: Long wire runs, high power, simple circuits
3. **Calculate Power Budget**: Ensure supply can handle load
- Add up all valve power consumptions
- Include inrush for AC valves (use 2x holding current)
- Add 20% safety margin
4. **Choose Enclosure**: Match environment
- Indoor clean: Open or conduit
- Industrial: DIN connector IP65
- Washdown/outdoor: IP67 terminal box
- Hazardous: Explosion-proof
5. **Specify Insulation Class**: Match temperature
- Ambient < 40°C: Class F (standard)
- Ambient 40-60°C: Class H
- High temp media: Consider Class H or special designs
### Installation Best Practices
**Wiring Guidelines:**
- Use wire gauge appropriate for current (typically 18-22 AWG for signal, 14-16 AWG for power)
- Keep wire runs as short as possible to reduce voltage drop
- Use shielded cable in electrically noisy environments
- Observe proper polarity for DC coils (reverse polarity can damage some types)
- Install fuses or circuit breakers to protect against short circuits
**Mounting Considerations:**
- Mount with solenoid coil vertical (upward) when possible to reduce sediment buildup
- Allow adequate clearance for coil removal/maintenance
- Avoid mounting in direct sunlight or near heat sources
- Ensure conduit entries point downward to prevent water ingress
- Use vibration dampeners in high-vibration applications
**Grounding and Safety:**
- Always ground metal valve bodies per local electrical codes
- Use ground fault protection where required
- Install emergency stop circuits for safety-critical applications
- Follow lockout/tagout procedures during maintenance
- Test emergency shutdown systems regularly
---
## Installation Best Practices
Proper installation is critical for reliable solenoid valve operation and long service life. Follow these industry best practices based on COVNA's 17+ years of valve manufacturing experience.
### Pre-Installation Checklist
**System Preparation:**
- [ ] Verify system pressure rating matches valve specifications
- [ ] Confirm fluid compatibility with valve materials
- [ ] Check voltage and power requirements match available supply
- [ ] Ensure pipe thread types match (BSP, NPT, etc.)
- [ ] Verify flow direction matches valve design
- [ ] Check for adequate clearance for operation and maintenance
**Valley Inspection:**
- [ ] Inspect valve for shipping damage
- [ ] Verify model number matches order specifications
- [ ] Check coil voltage rating label
- [ ] Confirm port sizes and thread types
- [ ] Test manual override (if equipped) for smooth operation
- [ ] Inspect seals for any visible damage
### Mounting Guidelines
**Orientation:**
- **Preferred**: Coil vertical, above the valve body
- **Acceptable**: Coil horizontal (for sizes up to 1/2")
- **Avoid**: Coil below valve body (risk of sediment in plunger tube)
**Positioning:**
- Allow minimum 6" (150mm) clearance for coil removal
- Position so electrical connections are accessible
- Avoid direct exposure to high heat sources
- Install vibration dampeners if mounted on vibrating equipment
**Support:**
- Support pipe weight independently of the valve
- Use pipe hangers upstream and downstream
- Never use valve as a structural support point
- Ensure stress-free installation (no pipe strain on valve)
### Piping Connection
**Thread Preparation:**
1. Clean pipe threads thoroughly
2. Apply appropriate thread sealant:
- PTFE tape for water, air, oil (wrap 3-4 turns, clockwise)
- Pipe dope for high-pressure applications
- Avoid sealants that react with media
3. Hand-tighten valve onto pipe
4. Use proper wrench on valve hex (not on coil or body)
5. Tighten 1-2 turns beyond hand-tight
6. Do NOT over-tighten (can crack body or distort seals)
**Flow Direction:**
- Check valve body for flow arrow marking
- Install with flow in direction of arrow
- For bi-directional valves, orientation may not matter
- Incorrect flow direction will prevent proper operation
### Electrical Connection
**Wiring Preparation:**
1. Verify power supply matches coil voltage
2. Use wire gauge appropriate for current draw:
- Up to 5A: 18 AWG (0.75mm²)
- 5-10A: 16 AWG (1.0mm²)
- 10-15A: 14 AWG (1.5mm²)
**Connection Steps:**
1. Remove coil enclosure or connector cover
2. Connect wires to appropriate terminals:
- AC coils: Line and neutral (polarity not critical)
- DC coils: Positive (+) and negative (-) - observe polarity
3. Ensure secure, tight connections
4. Replace enclosure/cover completely
5. Verify IP rating is maintained after connection
**Safety Considerations:**
- Install fuse or circuit breaker to protect circuit
- Use ground fault protection where required
- Ensure electrical code compliance
- Test emergency stop functionality
- Install lockout/tagout capability for maintenance
---
## Troubleshooting Common Issues
Even properly installed solenoid valves can experience problems. This troubleshooting guide from COVNA's technical team addresses the most common issues and their solutions.
### Problem: Valve Won't Open
**Symptoms**: No flow when energized, coil is powered
**Possible Causes and Solutions**:
| Cause | Check | Solution |
|-------|-------|----------|
| Insufficient voltage | Measure across coil terminals | Ensure voltage within ±10% of rating |
| Wrong voltage type | Verify AC/DC match | Replace coil with correct type |
| Damaged coil | Test coil resistance | Replace coil if open circuit or shorted |
| Pressure differential too low | Check minimum pressure rating | Increase system pressure or select direct-acting valve |
| Blocked orifice | Inspect valve internals | Clean or replace valve |
| Plunger stuck | Check for corrosion/debris | Clean or replace valve assembly |
| Incorrect flow direction | Check arrow on valve body | Reinstall with correct flow direction |
| Mechanical damage | Visual inspection | Replace damaged components |
**Diagnostic Steps**:
1. Verify power supply with multimeter (should read within ±10% of rating)
2. Check coil resistance (compare to manufacturer's specification)
3. Listen for audible "click" when energized (indicates mechanical operation)
4. Verify system pressure meets minimum requirement
5. Disassemble and inspect for blockages or damage
### Problem: Valve Won't Close
**Symptoms**: Continues to flow when de-energized
**Possible Causes and Solutions**:
| Cause | Check | Solution |
|-------|-------|----------|
| Residual magnetism | Test with different coil | Install demagnetizing circuit or replace coil |
| Stuck plunger | Manual operation check | Clean, lubricate, or replace |
| Damaged return spring | Visual inspection | Replace spring |
| Foreign object on seat | Disassembly inspection | Clean valve thoroughly |
| Worn or damaged seal | Visual inspection | Replace seals or valve |
| Excessive pressure | Check against rating | Reduce pressure or select higher-rated valve |
| Back pressure issue | System analysis | Install check valve or change configuration |
| Corroded components | Visual inspection | Replace affected parts |
### Problem: Coil Failure or Overheating
**Symptoms**: Coil burnout, excessive heat, insulation damage
**Possible Causes and Solutions**:
| Cause | Check | Solution |
|-------|-------|----------|
| Overvoltage | Measure supply voltage | Install voltage regulator or correct supply |
| Undervoltage | Measure supply voltage | Correct voltage supply |
| Continuous duty on intermittent coil | Check duty cycle rating | Replace with continuous duty coil or reduce duty cycle |
| High ambient temperature | Measure ambient | Relocate valve or use high-temp coil |
| Incorrect frequency | Verify AC frequency | Match coil to supply frequency |
| Moisture ingress | Inspect enclosure | Improve sealing, install drain, or relocate |
| Voltage spikes | Monitor with scope | Install surge suppressor |
| Wrong coil for application | Verify specifications | Select correct coil type and rating |
| Blocked valve (high pressure differential) | Check system pressure | Clean valve or select appropriate model |
### Problem: External Leakage
**Symptoms**: Fluid leaking from valve body, joints, or coil area
**Possible Causes and Solutions**:
| Location | Cause | Solution |
|----------|-------|----------|
| Port connections | Over/under tightening | Retorque to specification |
| Port connections | Damaged threads | Replace valve or use thread sealant |
| Port connections | Wrong thread type | Use appropriate adapter |
| Body seals | Worn or damaged O-rings | Replace seals |
| Body seals | Chemical incompatibility | Change seal material |
| Body seals | Excessive pressure/temperature | Select valve with higher rating |
| Coil area | Failed diaphragm | Replace diaphragm or valve |
| Coil area | Corroded plunger tube | Replace valve assembly |
| Coil area | Loose coil enclosure | Tighten or replace coil |
| Bleed ports | Clogged orifice | Clean orifice |
| Bleed ports | Excessive back pressure | Check system design |
### Problem: Slow Operation or Chattering
**Symptoms**: Delayed response, buzzing noise, erratic operation
**Possible Causes and Solutions**:
| Cause | Check | Solution |
|-------|-------|----------|
| Low voltage | Measure under load | Increase wire gauge, shorten run, or boost voltage |
| AC hum | DC coil vs AC supply | Use rectifier or switch to AC coil |
| Damaged shading ring | Visual inspection | Replace armature assembly |
| Restricted pilot orifice | Clean and inspect | Clean or replace components |
| High back pressure | System analysis | Install check valve or resize valve |
| Wrong valve type for application | Specification review | Select direct-acting or external pilot valve |
| Loose components | Physical inspection | Tighten or replace affected parts |
| Water hammer | System analysis | Install water hammer arrestor |
| Compressibility effects | Media analysis | Install accumulators or adjust timing |
---
## Maintenance and Longevity Tips
Proper maintenance significantly extends solenoid valve life and ensures reliable operation. COVNA recommends the following maintenance schedule based on 17+ years of field experience.
### Daily Checks
**Visual Inspection:**
- Check for external leaks at joints and connections
- Verify coil temperature (warm is normal, hot indicates problem)
- Listen for abnormal noises (buzzing, clicking, chattering)
- Observe response time (should be immediate when energized)
**Operational Verification:**
- Confirm valve opens fully when energized
- Verify complete closure when de-energized
- Check for proper flow direction
- Monitor system pressure stability
### Weekly Maintenance
**Cleaning:**
- Wipe down external surfaces
- Clean coil enclosure and electrical connections
- Remove debris from around valve
- Clear any blocked vents or drains
**Connection Inspection:**
- Check tightness of electrical terminals
- Verify pipe connections are secure
- Inspect for corrosion at connections
- Test grounding continuity
### Monthly Maintenance
**Functional Testing:**
- Cycle valve 10-20 times to verify smooth operation
- Measure response time (should be <100ms for most valves)
- Test under varying pressure conditions
- Verify seal integrity at maximum pressure
**Filter and Strainer Service:**
- Clean or replace inlet strainers
- Check for debris in filter housing
- Verify filter mesh integrity
- Monitor pressure drop across filter
### Quarterly Maintenance
**Component Inspection:**
- Remove and inspect internal components
- Check plunger for wear, scoring, or corrosion
- Inspect seals for cracks, hardening, or deformation
- Examine spring for fatigue or damage
- Verify orifice is clean and undamaged
**Electrical System Check:**
- Measure coil resistance (compare to specifications)
- Test insulation resistance (should be >1MΩ)
- Verify voltage at coil under load
- Check for voltage drops in wiring
- Test emergency stop and safety circuits
### Annual Overhaul
**Complete Disassembly and Inspection:**
- Break down valve completely
- Ultrasonic clean all metal parts
- Replace all seals and gaskets
- Inspect body for cracks or erosion
- Check threads for damage
- Measure critical dimensions
**Component Replacement:**
- Replace coil if resistance out of spec
- Replace plunger if any wear visible
- Replace spring if length or force out of spec
- Replace any damaged fasteners
- Update to current design improvements
**Testing and Certification:**
- Pressure test at 1.5x rated pressure
- Cycle test 1000 times
- Leak test with helium or bubble method
- Verify electrical safety standards
- Document all test results
### Environmental Considerations
**Temperature Management:**
- Install shade covers for outdoor valves in hot climates
- Use heat tracing for cold climates to prevent freezing
- Ensure adequate ventilation around coils
- Monitor ambient temperature and derate if necessary
**Protection from Elements:**
- Use weatherproof enclosures for outdoor installations
- Install drip legs to prevent water entering valve
- Use corrosion-resistant materials in marine environments
- Protect from UV radiation with shields or covers
**Vibration Control:**
- Use flexible connections to isolate valve from pipe vibration
- Install vibration dampeners on mounting brackets
- Avoid mounting on equipment with excessive vibration
- Check and tighten connections regularly in high-vibration areas
### Troubleshooting During Maintenance
**Document Everything:**
- Record baseline performance when valve is new
- Note any changes during routine maintenance
- Photograph wear patterns for analysis
- Track mean time between failures (MTBF)
- Compare performance to specifications
**Common Findings and Actions:**
| Finding | Likely Cause | Recommended Action |
|---------|--------------|-------------------|
| Seal hardening/cracking | Heat aging, chemical exposure | Upgrade seal material, reduce temperature |
| Plunger scoring | Contamination, dry operation | Add filtration, check lubrication |
| Spring fatigue | Excessive cycling, overstress | Use higher-rated spring, reduce cycling |
| Coil burnout | Overvoltage, high ambient temp | Check voltage, improve ventilation |
| Body corrosion | Chemical attack, galvanic | Change body material, add coating |
| Slow response | Low voltage, wear, contamination | Check power supply, clean/rebuild |
### Maintenance Records and Documentation
**Essential Records to Keep:**
- Installation date and initial test results
- Maintenance schedule and completion dates
- All inspections, findings, and actions taken
- Parts replaced with part numbers and dates
- Performance test results over time
- Any modifications or upgrades made
- Warranty information and service history
**Digital Tools:**
- Use CMMS (Computerized Maintenance Management System)
- Implement barcode or RFID tracking
- Set up automatic maintenance reminders
- Store photos and videos of inspections
- Create digital twins for complex systems
By following this comprehensive maintenance program, you can maximize solenoid valve reliability, minimize unplanned downtime, and achieve the lowest total cost of ownership for your fluid control systems.
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*This technical guide was prepared by the engineering team at COVNA GROUP CO., LTD. For application-specific recommendations or technical support, contact our valve specialists.*
