Low/High Temperatures [Classic 21 Series] 2/2, 3/2, & 4/2 Functions, 1/4" to 1-1/2" Port Sizes

Product Overview

The ROSS Controls is the Classic connection variant of the proven 21 Series inline poppet directional control valve platform, purpose-built for pneumatic systems that require reliable airflow control in extreme temperature environments. Covering a range from -40F (-40C) with Buna-N seals up to 300F (150C) with Fluorocarbon seals on pressure-controlled models, these valves deliver 2/2, 3/2, and 4/2 functions across port sizes from 1/4" to 1-1/2" with standard 1/2" conduit electrical connections.

The Series directional control valves regulate the direction, flow, and isolation of compressed air within pneumatic circuits. Available in both solenoid pilot controlled and pressure (pneumatic) controlled configurations, these valves leverage ROSS's signature poppet construction, a design that eliminates the sliding friction and wear mechanisms inherent in traditional spool-type valves. Both NPT and G (BSPP) thread options are available to meet North American and international installation standards.

The perpendicular poppet face seal geometry creates a high-flow path with positive shutoff, while the differential piston design delivers fast, consistent response times across millions of cycles. Fluorocarbon and Buna-N seal options extend the operational envelope to cover both low-temperature cold storage environments and high-temperature industrial process applications. The Classic 21 Series uses hardwired 1/2" conduit connections, making it ideal for permanent installations and applications where conventional conduit wiring is the preferred or required electrical interface.

For design engineers specifying pneumatic components in demanding thermal applications, the series provides a proven combination of extreme temperature tolerance, high flow capacity, self-cleaning poppet performance, and adaptability to vacuum service. The valves are readily adaptable to vacuum applications, and the solenoid models include a non-locking manual override as standard for commissioning and troubleshooting without tools.

Key Engineering Features

• Perpendicular Poppet Face Seals - Creates high-flow capacity with near-zero leakage and positive sealing, eliminating the bypass losses and sliding wear common in spool valves. The poppet seats at 90 degrees to the flow path, producing reliable shutoff on every cycle.
• Differential Piston Design - Delivers fast and consistent response times throughout the life of the valve. Surface areas of the piston poppet, exhaust poppet, and inlet poppet are precisely calculated to generate strong shifting and sealing forces in both directions, critical for high-cycle automation applications.
• Overwhelming Shifting Forces - Provides no-stick operation even after extended idle periods or in contaminated environments, ensuring reliable actuation every cycle. This is essential in extreme temperature applications where condensation or thermal cycling can cause sticking in lesser designs.
• Self-Cleaning High-Velocity Airflow - High-velocity air across poppet seats creates a natural cleaning action that continuously removes particulate contamination during valve operation, reducing unplanned downtime in harsh industrial settings and enabling reliable performance with less-than-ideal air quality.
• Superior Internal Guidance System with Self-Compensating Seals - Automatically adjusts poppet stroke length as seals experience normal wear, delivering extended service life without performance degradation. This feature is particularly valuable in extreme temperature service where seal materials experience greater thermal cycling stress.
• Extreme Temperature Range - Fluorocarbon seals enable media temperatures up to 300F (150C) for pressure-controlled models and up to 300F media with 180F ambient for solenoid models. Buna-N seals support low-temperature service down to -40F (-40C), covering cold storage, arctic outdoor, and refrigerated processing environments.
• Standard 1/2" Conduit Connection - Hardwired 1/2" conduit electrical connection with pre-wired leads provides a secure, vibration-resistant electrical interface suited for permanent installations. This classic connection type is compatible with standard industrial conduit systems and eliminates the need for separate connectors.
• Readily Adaptable to Vacuum Service - Specialized vacuum-rated models feature larger internal orifices that facilitate air transport with minimal differential pressure, enabling operation from full vacuum to 150 psig (10 bar). Mounting close to actuators reduces the volume of piping that must be pressurized or exhausted each cycle.
• Non-Locking Manual Override - Standard on all solenoid-controlled models for commissioning, troubleshooting, and system verification without requiring external tools or electrical power. Allows quick cycle testing during installation and fault diagnosis in the field.
• Downloadable CAD Models - Available for all variants to streamline machine design integration, facilitate interference checking, and reduce engineering lead time during new machine development and retrofit projects.

Technical Specifications

General Specifications

Temperature Ratings

The Series is specifically designed for operation outside standard temperature ranges. Seal material selection and actuation type determine the applicable temperature envelope. Solenoid pilot models are limited by coil thermal ratings at high ambient temperatures, while pressure-controlled models can operate at full media temperature in both ambient and media.

Important: For media temperatures below 40F (4C), compressed air must be free of water vapor to prevent ice formation inside the valve. Dry air supply to a dew point below the minimum operating temperature is required for reliable low-temperature service.

Electrical Data (Solenoid Pilot Valves)

All solenoid coils are rated for continuous duty. The Series Classic configuration uses 1/2" conduit connections with hardwired leads. Available AC and DC voltages are listed below. Encapsulated coil construction with Class F insulation ensures performance at high ambient temperatures.

Electrical Connection Options

Flow Performance Data

Flow performance data for representative 2/2 Solenoid Pilot controlled valve configurations. Cv values are rated at standard conditions. Response time formula applies to all functions; M and F constants vary by body size, function, and flow direction per the ROSS 21 Series catalog.

Response Time Formula: Response Time (ms) = M + (F x V), where M is the minimum response constant (ms), F is the fill or exhaust factor (ms/in3), and V is the downstream volume in cubic inches. M and F values are published per port size and function in the ROSS 21 Series catalog.

Certifications & Compliance

Typical Applications & Industries

Metals Processing and High-Temperature Manufacturing

• Steel furnaces, hot rolling mills, annealing lines, galvanizing, and continuous casting where ambient and media temperatures routinely exceed 180F. The Fluorocarbon seal option on pressure-controlled models ensures reliable operation in sustained high-heat environments up to 300F.
• Thermoforming and plastics manufacturing for controlling vacuum and pressure air in heated mold zones where standard seals would degrade over time.
• Glass manufacturing for directional air control near furnaces and forming stations operating at extreme temperatures.
• Foundry operations for controlling pneumatic cylinders and actuators in proximity to molten metal operations requiring high-temperature seal materials.

Cold Storage, Food and Beverage Processing

• Cold storage and refrigeration facilities operating pneumatic actuators in freezer environments down to -40F. Buna-N seals maintain flexibility and sealing integrity at sub-freezing temperatures where standard seal materials become brittle.
• Food and beverage processing including blast freezing, cryogenic packaging, and cold chain automation lines where reliable valve performance at low temperatures is essential to throughput.
• Grain handling and agricultural processing where outdoor installations in cold climates require proven low-temperature operation and positive sealing.

Automotive and Assembly Manufacturing

• Automotive body shop actuators, paint line controls, and assembly automation where reliable cycling and dirt tolerance reduce maintenance intervals and improve line availability.
• Assembly and test operations including leak testing, vacuum pick-and-place, and channel-select test fixtures requiring precise directional air control at high cycle rates.
• Stamping press controls and welding fixture actuators in environments subject to thermal variation, coolant exposure, and contamination.

Packaging and Material Handling

• Vacuum packaging, case erecting, carton sealing, and palletizing systems benefiting from the high-flow, self-cleaning poppet design and consistent response times.
• Material lifting and handling via vacuum cup gripper systems where vacuum service adaptability allows the series to serve both pressure and vacuum functions.
• Pick-and-place and part orientation systems in packaging lines requiring fast valve response and reliable operation over millions of cycles.

Hazardous Locations and Process Industries

• Petrochemical and oil and gas processing facilities where explosion-proof or intrinsically safe variants are specified for Class I Division 1 and 2 environments with flammable gases or vapors.
• Chemical manufacturing and pharmaceutical production in solvent-rich or combustible powder environments requiring FM, CSA/UL, and ATEX certified pneumatic controls.
• Paint spray booths and coating operations with flammable solvent vapors requiring certified explosion-proof directional control valves.
• Outdoor pipeline control installations in arctic climates where both low-temperature seal performance and explosion-proof certification are simultaneously required.

General Industrial and Semiconductor

• Semiconductor and electronics manufacturing for clean air directional control in temperature-controlled process zones where reliable isolation and near-zero leakage are required.
• Pharmaceutical manufacturing for tablet press automation, packaging equipment, and material transfer systems in cleanroom and controlled environments.
• General pneumatic automation across manufacturing and process industries where extreme temperatures, vacuum service, or hazardous location classification require more than a standard-temperature valve.

Ordering and Model Number Configuration

The ROSS 21 Series uses a structured model number system. The Series Classic connection valves follow the same nomenclature as the full 21 Series platform. Below is a representative breakdown for a 2/2 solenoid pilot controlled valve with standard conduit connection.

Voltage codes: W = 24 VDC, Z = 110/120 VAC/60 Hz, Y = 220/240 VAC/60 Hz.

Seal material codes: 1 = Fluorocarbon (high temperature), 2 = Buna-N (low temperature).

For G (BSPP) threads, add "D" as a prefix to the model number (e.g., D2171B2001W for G threads).

Low-temperature solenoid options are available in 3/8 and 3/4 body sizes. High-temperature pressure-controlled models support ambient and media temperatures up to 300F (150C).

For external pilot supply, a different body/port code is used in the model number. Contact ROSS Controls for the correct model number when specifying external pilot.

Explosion-proof and intrinsically safe variants use an "E" prefix in the model number designation. Consult the ROSS 21 Series catalog for complete explosion-proof model configurations.

Body Size and Port Size Reference

Valve Function Codes

Accessories

Exhaust Silencers

Aluminum exhaust silencers are available for port sizes 1/2", 1", and 1-1/2", rated to 290 psig (20 bar). These thread directly onto the exhaust port to reduce exhaust noise in the surrounding environment.

Warning: Exhaust silencers must have flow capacities at least as great as the exhaust capacities of the valves. Contaminated or obstructed silencers can cause increased back pressure, affecting valve response and causing erratic operation.

Manual Override Kits

Field-installable non-locking manual override button kits are available for most 21 Series models. Non-locking actuation allows the valve to be manually shifted for testing and commissioning; the valve returns to its default position when the button is released.

Indicator Light Kits

LED visual indicator light kits are available for integration into the solenoid housing, providing a clear visual indication of solenoid energization status. Available for 24 VDC, 120 VAC, and 230 VAC circuits to support commissioning and troubleshooting.

Mounting Brackets

Support brackets are available for securing inline-mounted valves in vertical or horizontal orientations, reducing stress on piping connections in high-vibration or high-cycle applications. Custom brackets are available for specific installation configurations.

Related Products & Accessories

• 2759 Series - Low/High Temperature DIN/M12 Connection 21 Series - DIN EN 175301-803 and M12 quick-disconnect connection variant of the same 21 Series platform. Preferred for applications where rapid coil replacement without hardwired connections is required. https://www.rosscontrols.com/en/series/2759-lowhigh-temperatures-din-m12-connection-21-series
• 230 Series - Standard Temperatures Classic 27 Series - Classic 27 Series inline poppet valves for standard temperature applications with port sizes up to 2-1/2" for higher flow requirements beyond the 21 Series range. https://www.rosscontrols.com/en/series/230-standard-temperatures-classic-27-series
• 2760 Series - Vacuum Low/High Temperatures DIN/M12 21 Series - Vacuum-rated variant of the 21 Series with DIN and M12 connections for vacuum applications in extreme temperature environments. https://www.rosscontrols.com/en/series/2760-vacuum-low-high-temperatures-din-m12-connection-21-series
• Exhaust Silencers - Aluminum exhaust silencers rated to 290 psig for port sizes 1/2" through 1-1/2" to reduce exhaust noise at valve exhaust ports. https://www.rosscontrols.com/en/series/90-silencers
• Lockout Valves (Energy Isolation) - L-O-X lockout valves for safe pneumatic energy isolation during maintenance, compliant with OSHA lockout/tagout requirements. https://www.rosscontrols.com/en/series/1287-lockout-valves-15-series
• Electrical Connectors - DIN EN 175301-803 Form A and Form B connectors, prewired assemblies, and lighted indicator connectors for ROSS solenoid valves. https://www.rosscontrols.com/en/series/91-electrical-connectors

Frequently Asked Questions (FAQ)

Q: What is the series and how does it differ from the 2759 Series?

A: The Series is the Classic connection variant of the ROSS 21 Series, using standard 1/2" conduit with hardwired leads as the electrical interface. The 2759 Series uses DIN EN 175301-803 and M12 quick-disconnect connectors instead. Both series share the same poppet valve body, temperature range, flow performance, and seal options. The choice between them depends on the preferred electrical connection method: conduit for permanent hardwired installations versus quick-disconnect for easier coil replacement and commissioning.

Q: What is the maximum operating temperature for the series?

A: The highest-rated configuration is a pressure-controlled valve with Fluorocarbon seals, which supports ambient and media temperatures up to 300F (150C). For solenoid pilot models with Fluorocarbon seals, maximum media temperature is 300F but ambient is limited to 180F (82C) due to solenoid coil thermal ratings. Always verify the coil temperature rating matches the application ambient before specifying solenoid models for high-temperature service.

Q: What is the minimum operating temperature for the series?

A: With Buna-N seals, low-temperature models operate down to -40F (-40C) for both ambient and media conditions. Buna-N maintains seal flexibility and sealing integrity at these sub-freezing temperatures. For applications below 40F (4C), compressed air supply must be dried to a dew point below the minimum operating temperature to prevent ice formation inside the valve.

Q: Which seal material should I select for my application?

A: Choose Fluorocarbon seals for high-temperature applications where media or ambient temperatures exceed the standard range, up to 300F (150C) for pressure-controlled models. Choose Buna-N seals for low-temperature applications down to -40F (-40C). Buna-N is also a cost-effective option for moderate temperature service in standard compressed air. If your application involves chemical exposure in addition to temperature extremes, Fluorocarbon provides superior chemical resistance.

Q: Can the series be used in vacuum applications?

A: Yes. The 21 Series is readily adaptable to vacuum service. Specialized vacuum-rated models feature larger internal orifices that enable air transport with minimal differential pressure, operating from full vacuum to 150 psig (10 bar). Mounting the valve as close as possible to the actuator minimizes the downstream volume that must be pressurized or exhausted each cycle, improving response time in vacuum applications.

Q: Are NPT and G (BSPP) thread options both available?

A: Yes. Standard models ship with NPT threads for North American installations. To order with G (BSPP) threads for European and international systems, add a "D" prefix to the model number. Both thread options deliver equivalent valve performance; the selection is based on regional installation standards and existing piping infrastructure.

Q: What pilot supply pressure is required?

A: For internal pilot supply configurations, the inlet pressure must meet the minimum 30 psig (2 bar) operating threshold; pilot pressure is automatically derived from the inlet. For external pilot supply configurations, pilot pressure must be equal to or greater than inlet pressure and must satisfy the 30 psig minimum. Vacuum service models using external pilot require a minimum of 30 psig pilot supply regardless of inlet conditions.

Q: Do these valves require lubrication in the air supply?

A: The Series valves do not require lubrication in the air supply for normal operation. However, if lubrication is used, only petroleum-based lubricants with an aniline point between 180F and 220F and ISO 32 viscosity or lighter should be applied. Avoid lubricants with phosphate-type additives, as these can degrade elastomeric seals and lead to premature failure. Do not use synthetic lubricants, which are incompatible with the seal materials.

Q: Can the valve be converted between internal and external pilot supply in the field?

A: Yes. ROSS 21 Series valves can be field-converted from internal to external pilot supply by relocating the pipe plug between the external pilot port and the internal pilot passage. Contact ROSS Controls for the updated model number to maintain proper system documentation after conversion.

Q: What filtration is recommended for the air supply?

A: ROSS recommends filtered compressed air with 5-micron particulate filtration upstream of the valve. While the poppet construction provides excellent dirt tolerance compared to spool valves, proper filtration maximizes valve service life and maintains consistent performance. For sub-freezing applications, an appropriate coalescing filter and dryer are also required to prevent moisture and ice accumulation.

Q: Are explosion-proof or hazardous location variants available?

A: Yes. The 21 Series includes explosion-proof and intrinsically safe variants certified for Class I Division 1 and 2 hazardous locations per FM and CSA/UL standards, and ATEX certified for European Zones 1 and 2. These models use an "E" prefix in the model number and feature heavier-duty explosion-proof coil enclosures or energy-limited intrinsically safe coil designs. The 21 Series explosion-proof valves are specifically rated for low-temperature environments down to -4F (-20C), with arctic options available to -40F (-40C).

Q: What valve functions are available in the series?

A: The Series is available in 2/2 (two-way, two-position), 3/2 (three-way, two-position), and 4/2 (four-way, two-position) functions. The 2/2 and 3/2 functions are offered in both normally closed and normally open configurations. The 4/2 function provides bidirectional control for double-acting cylinders and actuators.

Q: How do I calculate valve response time for my application?

A: Use the formula: Response Time (ms) = M + (F x V), where M is the minimum valve response constant in milliseconds, F is the fill or exhaust factor in ms per cubic inch, and V is the downstream volume in cubic inches. M and F values are published for each body size and function in the ROSS 21 Series catalog. This formula allows accurate prediction of actual system response times for sizing and cycle time calculations.

Installation & Maintenance Guidelines

• Mount inline in any orientation; vertical mounting with the pilot or solenoid assembly oriented upward is preferred for optimal condensate drainage and heat dissipation from the coil.
• Supply filtered compressed air with 5-micron particulate filtration to maximize valve service life. Although the poppet design provides superior dirt tolerance, proper filtration prevents contamination from interfering with poppet sealing over time.
• Do not restrict supply lines or exhaust ports below the flow capacity needed for the application. Restrictions can reduce pressure below the 30 psig minimum operating threshold and cause erratic or failed actuation.
• For external pilot supply configurations, pilot pressure must be equal to or greater than inlet pressure and must satisfy the 30 psig minimum. Use a separate filtered supply if inlet pressure cannot meet these requirements.
• In sub-freezing applications below 40F (4C), compressed air must be free of water vapor to prevent ice formation inside the valve. Use a refrigerated dryer or desiccant dryer sized to deliver a dew point below the minimum operating temperature.
• Use only petroleum-based lubricants with an aniline point between 180F and 220F (82C to 104C) and ISO 32 viscosity or lighter if lubrication is added to the air supply. Lubricants with phosphate-type additives must be avoided as they degrade seal materials.
• For high-temperature solenoid applications, verify that the ambient temperature at the valve and coil location does not exceed 180F (82C). Pressure-controlled models without solenoids are not subject to this restriction and may be used up to 300F (150C) ambient.
• Verify that exhaust silencers have flow capacities at least as great as the exhaust capacities of the valves. Check and clean silencers periodically. Contaminated or blocked silencers increase back pressure, which can cause sluggish or incomplete valve shifting.
• When wiring the 1/2" conduit connection, ensure all electrical connections are made per applicable electrical codes and local regulations. For hazardous location installations, conduit seals must be installed as required by the NEC (NFPA 70) or applicable local code.
• Verify that the solenoid coil voltage matches the electrical supply voltage before energizing. Applying incorrect voltage can damage the coil. All solenoid coils are rated for continuous duty; do not use on intermittent-only rated circuits.
• After installation, test valve operation using the manual override button (solenoid models) before connecting to the control system to confirm the valve shifts and seals correctly under supply pressure.
• Perform all maintenance and service operations only after shutting down the pneumatic system, exhausting all pressure to zero, and completing lockout/tagout procedures per OSHA 1910.147 and EN 1037 standards. Never service a pressurized valve.
• Use only genuine ROSS replacement parts for any repair or overhaul. Substituting non-OEM components can compromise valve performance and void safety certifications. After any overhaul, perform a functional test before returning the valve to service.

Warranty & Global Support

ROSS Controls provides a one-year warranty on all products, covering defects in material and workmanship from the date of purchase. Warranty obligations include repair, replacement, or refund of purchase price for products determined by ROSS to be defective.

Warranty coverage is void if products have been subject to misuse, misapplication, improper maintenance, modification, unauthorized repair, or operation outside published specification limits. Products requiring warranty service must be returned freight prepaid to a ROSS facility.

Global technical support is available through ROSS Controls offices in the USA (headquarters in Ferndale, Michigan), Canada, Brazil, Germany, France, United Kingdom, India, China, and Japan.

Contact ROSS Controls USA at (800) 438-7677 or visit rosscontrols.com for product configuration assistance, technical support, distributor locator services, and CAD model downloads.

For complete technical data, dimensional drawings, performance curves, and valve configurator access, visit the ROSS Controls product page or contact ROSS Controls directly.

Download Catalog: https://www.rosscontrols.com/en/documents/393/