Vacuum, 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 a family of vacuum-rated inline poppet directional control valves within the proven 21 Series platform, designed for pneumatic and vacuum systems that demand reliable flow control across extreme temperature environments spanning -40F (-40C) to 300F (150C). Using classic 1/2" conduit electrical connections with integral leads, these TUV-certified (SIL 2) valves are offered in 2/2, 3/2, and 4/2 functions in port sizes from 1/4" to 1-1/2", with maximum flow capacity reaching Cv 33 (32,000 Nl/min). The Series is the conduit-connection counterpart to the 2760 Series, which uses DIN and M12 quick-disconnect connections.

The key differentiator of the series is its engineered suitability for vacuum service. ROSS vacuum valves feature larger orifices than standard positive-pressure valves, enabling greater flow capacity despite the small differential between the reduced internal pressure and ambient atmospheric pressure outside the valve. In vacuum applications, atmospheric pressure pushes air into the valve rather than the valve pulling air in, and the poppet design fully accommodates this reversed force balance. These valves serve vacuum lifting, holding, vacuum packaging, transport of fine particles, and leak testing across both vacuum-pump and venturi-sourced circuits.

The Series also supports full vacuum operation, where compressed air is unavailable and the valve actuates solely on the force differential between atmospheric pressure at port 1 and 10 to 30 inches of Mercury vacuum inside the valve body. Fluorocarbon and Buna-N seal options extend the operational envelope to cover high-temperature processes up to 300F and low-temperature cold storage or arctic environments down to -40F, making the series applicable in industries from metals processing and glass manufacturing to cryogenic packaging and semiconductor handling.

For design engineers specifying pneumatic or vacuum components in demanding applications, the series provides a unique combination of vacuum capability, extreme temperature tolerance, high flow capacity, SIL-rated safety performance, and the installation flexibility of a hardwired 1/2" conduit connection suited for locations where quick-disconnect coil plugs are impractical or subject to vibration-induced disconnection.

Key Engineering Features

• Vacuum-Rated Larger Orifice Design - Engineered with oversized orifices to maximize flow under the small pressure differentials characteristic of vacuum service, enabling faster cycle times and more efficient vacuum lifting, packaging, and transport operations.
• Full Vacuum Actuation Capability - Supports operation where no compressed air is available; the valve shifts using the force differential between atmospheric pressure at port 1 and 10 to 30 inches Hg vacuum in the valve body, eliminating the need for a separate compressed air supply.
• Perpendicular Poppet Face Seals - Creates high-flow capacity with near-zero leakage and positive sealing at 90 degrees to the flow path, eliminating the bypass losses and sliding-wear failures common in spool valves.
• Differential Piston Design - Precisely calculated piston, inlet poppet, and exhaust poppet surface areas generate overwhelming shifting forces in both directions, delivering fast and consistent response times throughout the valve's full service life.
• Self-Cleaning High-Velocity Flow Path - Maximum air velocity occurs across the poppet seat interface, where airflow continuously expels particulate contamination, scale, and debris. This self-cleaning action provides strong dirt tolerance and extends maintenance intervals in harsh environments.
• Self-Compensating Seal Technology - Superior internal guidance adjusts poppet stroke length automatically as seals wear, maintaining consistent sealing force and near-zero leakage without manual adjustment or premature replacement.
• Classic 1/2" Conduit Connection with Integral Leads - Hardwired 1/2" NPT conduit entry with 30" integral leads provides a secure, vibration-resistant electrical connection suited for installations subject to shock, vibration, high washdown pressure, or where DIN plug retention is a concern.
• Extreme Temperature Seal Options - Fluorocarbon seals extend high-temperature operation to 300F (150C) media; Buna-N seals maintain flexibility and sealing integrity at low temperatures down to -40F (-40C), covering the full range of cold storage, arctic, furnace, and process heat applications.
• Non-Locking Manual Override - Standard on all solenoid pilot controlled models for commissioning, troubleshooting, and functional verification without electrical power or external tools.
• TUV SIL 2 Certification (SIL 3 in Redundant Configuration) - Certified by TUV Rheinland per IEC 61508 and IEC 61511 for integration into safety-related control architectures, achieving Performance Level c in singular (HFT=0) and Performance Level e in redundant (HFT >= 1) configurations per EN ISO 13849-1.

Technical Specifications

General Specifications

Temperature Ratings

The Series is specifically designed for operation outside the standard temperature range. Seal material selection determines the applicable temperature envelope. The conduit coil option is required for the high-temperature solenoid configuration.

Important: For media temperatures below 40F (4C), compressed air must be completely free of water vapor to prevent ice formation inside the valve body. For vacuum service at sub-freezing temperatures, the vacuum source and interconnecting lines must similarly be free of moisture.

Electrical Data (Solenoid Pilot Valves)

All solenoids are rated for continuous duty with an IP65 enclosure rating. The conduit connection provides a sealed, vibration-resistant installation suited for high-cycle or high-washdown environments.

Electrical Connection Options

Flow Performance Data

Flow performance data for 2/2 Solenoid Pilot Controlled vacuum valves (select body sizes shown). Vacuum-rated valves incorporate larger orifices than standard-pressure variants to compensate for low differential pressure in vacuum service.

Response Time Formula: Response Time (ms) = M + (F x V), where M is the minimum response constant (milliseconds), F is the fill/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

Vacuum Lifting, Holding, and Material Handling

• Vacuum pick-and-place systems for lifting, repositioning, and releasing large flat panels, sheet metal, glass, cardboard, and formed plastic parts using vacuum cup arrays controlled by 2/2 or 3/2 valve configurations.
• Vacuum gripping on robotic end-effectors for part loading, unloading, and in-process transport where the series' conduit connection resists coil separation under vibration and repeated arm motion.
• Vacuum holding fixtures for machining, welding, and assembly operations requiring stable, repeatable part location without mechanical clamping that could damage surfaces.
• Bulk material conveying using venturi-sourced vacuum for transporting powders, granules, pellets, and small particles through pneumatic conveying lines where contaminated airflow is present.

Vacuum Packaging and Food Processing

• Modified atmosphere and vacuum packaging lines for food, medical devices, and industrial components where 3/2 valve cycling controls evacuation and backfill sequences at high repetition rates.
• Cryogenic and blast-freeze environments where Buna-N seal variants maintain sealing integrity at temperatures down to -40F, enabling vacuum-assisted packaging in cold-chain automation lines.
• Product transfer and orientation for food processing lines operating in high-washdown zones where the sealed conduit connection withstands repeated cleaning cycles that would compromise unpotted DIN connectors.
• Pharmaceutical and nutraceutical container filling and sealing where vacuum control must be precise and leak testing is required before final seal application.

Metals, Glass, and High-Temperature Processing

• Vacuum forming and handling of glass blanks and flat glass at or near furnaces and lehr zones operating above 180F ambient, where Fluorocarbon-sealed pressure-controlled variants operate up to 300F media and ambient.
• Steel mill and foundry auxiliary pneumatic circuits requiring vacuum capabilities for mold venting, degassing, or part removal from tooling at elevated temperatures.
• Thermoforming and plastics manufacturing for vacuum draw-down into heated molds where standard Buna-N seals would degrade, and the Fluorocarbon seal option maintains sealing integrity throughout the thermal cycle.
• Annealing and heat treatment chamber valve control in environments where high ambient temperatures preclude standard seal materials.

Semiconductor, Electronics, and Cleanroom

• Wafer handling and vacuum chuck control in semiconductor fabrication where repeatable, near-zero-leakage sealing at the valve is critical to maintaining process vacuum levels.
• Electronic component pick-and-place on SMT assembly lines requiring fast, reliable vacuum switching with low dead volume to minimize latency between valve command and vacuum application at the nozzle.
• Cleanroom material transport carts and FOUP handling systems where the valve's self-cleaning poppet design reduces contamination risk compared to spool valves that shed wear debris.
• Temperature-controlled process chambers in microelectronics manufacturing where extreme temperature seal options accommodate process environments outside the range of standard valves.

Leak Testing and Quality Control

• Pressure decay and vacuum decay leak testing fixtures for automotive components, sealed assemblies, medical devices, and consumer electronics where precise isolation and fast venting are required.
• Multi-channel test stands using 2/2 normally closed configurations to selectively connect vacuum or pressure sources to test ports, with the valve's near-zero leakage ensuring test integrity.
• In-line quality control systems integrated into production equipment where the series conduit connection provides permanent, tamper-resistant wiring in test stand enclosures.
• Cold-room leak testing for refrigeration components and sealed containers where low-temperature Buna-N seal variants maintain consistent valve performance without seal stiffening.

Outdoor, Arctic, and Cold Storage Infrastructure

• Pipeline control and processing facilities in arctic or sub-freezing climates where ambient temperatures drop below -40F and standard valve seals become brittle and leak.
• Cold storage warehouse automation including conveyor diverters, pallet handlers, and pneumatic door actuators where Buna-N seals rated to -40F maintain full flexibility and sealing capability.
• Outdoor industrial installations in northern climates where the hardwired conduit connection eliminates the risk of moisture ingress through DIN plug interfaces in freeze-thaw cycling environments.
• Refrigerated transport loading and unloading equipment requiring reliable pneumatic valve function during continuous exposure to sub-zero temperatures.

Ordering and Model Number Configuration

The ROSS 21 Series uses a structured model number system that encodes all valve configuration parameters. The Series uses the classic 1/2" conduit coil connection (coil codes 4 and 6). Below is the model number breakdown for a solenoid pilot controlled valve in this series.

Voltage codes: H = 12 VDC, W = 24 VDC, Z = 120 VAC/60 Hz, Y = 240 VAC/60 Hz.

Coil codes for Series classic conduit connection: 4 = 1/2" conduit with 30" leads (standard temperature); 6 = 1/2" conduit with 30" leads (high temperature, Fluorocarbon seals required).

Seal codes: 1 = Fluorocarbon (high temperature, up to 300F media); 2 = Buna-N (low temperature, down to -40F).

For G (BSPP) threads, add "D" as a prefix to the model number (e.g., D2171B2001W-4). Low-temperature solenoid configurations are available in 3/8 and 3/4 body sizes.

For pressure (pneumatic) controlled configurations, replace actuation code 7 with 5. Pressure-controlled variants do not use coil codes and are not voltage-dependent.

Internal pilot supply is standard. External pilot supply configurations are available; contact ROSS for the applicable model number suffix.

Accessories

Exhaust Silencers

Aluminum exhaust silencers are available for port sizes 1/2", 1", and 1-1/2", rated to 290 psig (20 bar). For vacuum service applications, ensure that any installed silencer does not introduce backpressure that reduces vacuum level below the required threshold.

Warning: Exhaust silencer flow capacity must be equal to or greater than the valve's exhaust flow capacity. Contaminated silencers cause backpressure that adversely affects valve response and vacuum level. In vacuum service, verify that silencer installation does not introduce leakage paths that compromise vacuum integrity.

Indicator Light Kits

Optional indicator light kits provide visual verification of solenoid energization status, simplifying commissioning and troubleshooting. Available for 24 VDC, 110 to 120 VAC, and 230 VAC supply voltages. Kits are designed to mount on the valve solenoid housing without modification to the valve body.

Manual Override Options

Beyond the standard non-locking push-button override included with solenoid pilot models, ROSS offers locking override buttons and extended button assemblies for applications requiring sustained manual hold or operation from a safe distance from moving machinery.

Related Products & Accessories

• 231 Series - Low/High Temperatures Classic 21 Series (Non-Vacuum) - Standard positive-pressure 1/2" conduit connection 21 Series valves for extreme temperature applications without vacuum service requirement. https://www.rosscontrols.com/en/series/231-low-high-temperatures-classic-21-series
• 2760 Series - Vacuum, Low/High Temperatures, DIN & M12 Connection 21 Series - Vacuum-rated 21 Series variant with DIN EN 175301-803 and M12 quick-disconnect connections for applications where rapid coil swap is preferred. https://www.rosscontrols.com/en/series/2760-vacuum-low-high-temperatures-din-m12-connection-21-series
• 2759 Series - Low/High Temperatures DIN & M12 Connection 21 Series (Non-Vacuum) - Non-vacuum DIN and M12 connection 21 Series valves for extreme temperature service with quick-disconnect coil interface. https://www.rosscontrols.com/en/series/2759-lowhigh-temperatures-din-m12-connection-21-series
• 230 Series - Standard Temperatures Classic 27 Series - Standard temperature inline poppet valves with port sizes up to 2-1/2" for higher flow requirements in moderate temperature environments. https://www.rosscontrols.com/en/series/230-standard-temperatures-classic-27-series
• Exhaust Silencers - Aluminum silencers rated to 290 psig for port sizes 1/2" through 1-1/2" to attenuate exhaust noise on valve discharge ports. https://www.rosscontrols.com/en/series/90-silencers
• Lockout Valves (Energy Isolation) - L-O-X lockout valves for safe energy isolation during maintenance per OSHA lockout/tagout requirements, compatible with 21 Series installations. https://www.rosscontrols.com/en/series/1287-lockout-valves-15-series

Frequently Asked Questions (FAQ)

Q: What makes the series different from the 231 Series?

A: Both the and 231 Series use classic 1/2" conduit connections and cover the same extreme temperature range. The Series is specifically engineered for vacuum service, incorporating larger-orifice poppet designs that maintain adequate flow under the low differential pressure conditions characteristic of vacuum applications. The 231 Series is optimized for positive-pressure service only.

Q: What makes the series different from the 2760 Series?

A: Both series are vacuum-rated and cover the same temperature range with the same internal poppet valve mechanism. The key distinction is the electrical connection: the series uses classic 1/2" conduit with integral 30" leads (hardwired), while the 2760 Series uses DIN EN 175301-803 Form A/B or M12 quick-disconnect connectors. The conduit connection in the series is better suited for high-vibration, high-washdown, or permanent-installation applications where plug retention is a concern.

Q: What vacuum level can the series valves handle?

A: The Series operates from full vacuum (approximately 29.9 inches Hg, or roughly -14.7 psig) up to 150 psig positive pressure. For full vacuum actuation (no compressed air available), the valve requires 10 to 30 inches Hg vacuum in the valve body to generate sufficient differential force for shifting.

Q: What is a full vacuum valve and when should I specify one?

A: A full vacuum valve shifts using only the differential force between atmospheric pressure at port 1 and the vacuum level inside the valve body (10 to 30 inches Hg). This configuration is ideal when compressed air is unavailable, such as in cleanroom installations, battery-operated mobile equipment, or food processing lines where introducing compressed air is undesirable. Full vacuum valves are offered in 3/2 configurations within the 21 Series platform.

Q: What seal material should I select?

A: Select Fluorocarbon seals for high-temperature applications where media temperature reaches up to 300F (150C). Select Buna-N seals for low-temperature applications down to -40F (-40C). For ambient temperatures between 0F and 122F with standard media temperatures, either seal material is acceptable based on chemical compatibility requirements. Note that the high-temperature conduit coil (code 6) requires Fluorocarbon seals.

Q: Can these valves be used in both vacuum and positive pressure in the same circuit?

A: Yes. The Series is rated from full vacuum through 150 psig, so a single valve can control circuits that alternate between vacuum and positive pressure, such as vacuum pick-and-place systems that use vacuum to grip a part and then a positive-pressure pulse to release it. Verify that all connected tubing, fittings, and actuators are rated for the full pressure range of the application.

Q: What is the maximum operating temperature?

A: For pressure-controlled models with Fluorocarbon seals, both ambient and media temperatures can reach 300F (150C). For solenoid pilot models, the media temperature maximum is 300F with an ambient limit of 180F (82C) because the solenoid coil must not exceed this ambient threshold.

Q: What is the minimum operating temperature?

A: With Buna-N seals, the low-temperature models operate down to -40F (-40C) for both ambient and media. This makes them suitable for arctic outdoor installations and cold-storage automation operating in blast-freeze or cryogenic environments.

Q: Can these valves be used in safety-critical (SIL-rated) applications?

A: Yes. The 21 Series is TUV Rheinland certified to SIL 2 (IEC 61508 and IEC 61511) and PL c (EN ISO 13849-1) in a singular configuration (HFT = 0). In a redundant 1oo2 arrangement (HFT = 1 or greater), the system can achieve SIL 3 and PL e, supporting the highest level of pneumatic safety integrity for vacuum-assisted machine guarding and press safety applications.

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

A: Yes. Standard models ship with NPT threads. To order with G (BSPP) threads, add "D" as a prefix to the model number. For example, the NPT model 2171B2001W-4 becomes D2171B2001W-4 in G thread.

Q: What pilot supply pressure is required?

A: For internal pilot supply, the inlet pressure must meet the minimum 30 psig operating threshold. For external pilot supply configurations, the pilot signal pressure must equal or exceed the inlet pressure and must also meet the minimum operating pressure. In vacuum service where inlet pressure is below atmospheric, external pilot supply is typically required to provide adequate shifting force.

Q: Do Series valves require lubrication?

A: The valve does not require air line lubrication for standard operation. If lubrication is used in the compressed air system, use only petroleum-based lubricants with an aniline point between 180F and 220F (82C to 104C), ISO 32 viscosity or lighter, at approximately one drop per minute. Avoid phosphate-type additives, which damage elastomeric components.

Q: Can the pilot supply be converted from internal to external in the field?

A: Yes. ROSS 21 Series valves can be field-converted by relocating the pipe plug between the external pilot port and the internal pilot passage. This is particularly useful in vacuum service, where inlet pressure is below atmospheric and an external compressed air pilot supply is needed for reliable actuation. Contact ROSS for the updated model number to maintain accurate documentation.

Q: Are 3D CAD models available?

A: Yes. Downloadable CAD models are available for Series variants through the ROSS Controls website at rosscontrols.com, supporting direct import into mechanical design software for interference checking, assembly documentation, and installation planning.

Q: How do I calculate the valve response time for my vacuum system?

A: Use the formula: Response Time (ms) = M + (F x V), where M is the minimum response constant in milliseconds, F is the fill/exhaust factor in ms per cubic inch, and V is the downstream volume in cubic inches being evacuated or pressurized. In vacuum service, the small differential pressure means effective volume evacuation time will be longer than in equivalent positive-pressure applications even with larger orifices; verify system timing requirements against calculated values using the M and F constants from the ROSS 21 Series catalog.

Installation & Maintenance Guidelines

• Mount inline in any orientation; vertical mounting is preferred for optimal poppet seating, condensate drainage, and consistent valve response.
• Supply filtered air (5-micron filtration minimum) to the valve inlet to maximize service life and prevent particulate contamination from lodging on poppet seats. In vacuum service, install filtration on both the vacuum source line and any compressed air pilot supply lines.
• Do not restrict supply lines or exhaust ports beyond the flow capacity of appropriately sized silencers. Backpressure on exhaust ports reduces valve response speed and, in vacuum circuits, can limit achievable vacuum level.
• For vacuum service circuits, verify that all downstream tubing, fittings, connectors, and actuators are rated for the full vacuum level and have sufficient vacuum-tight sealing to prevent false ingress of atmospheric air that would degrade system vacuum.
• When internal pilot supply is used in vacuum service, confirm that inlet pressure is sufficient (minimum 30 psig positive) to actuate the valve. If the inlet operates at vacuum or low positive pressure, configure the valve for external pilot supply using a separate compressed air pilot source.
• For external pilot supply configurations, pilot pressure must equal or exceed inlet pressure and meet the minimum operating pressure of 30 psig.
• For media or ambient temperatures below 40F (4C), compressed air and vacuum system media must be free of water vapor to prevent ice formation inside the valve. Verify that compressed air dewpoint is below the minimum operating temperature.
• Use only petroleum-based lubricants with an aniline point between 180F and 220F (82C to 104C), ISO 32 viscosity or lighter. Avoid all phosphate-type additives, which degrade elastomeric seals.
• Verify that installed exhaust silencers have flow capacities at least equal to the valve's exhaust capacity. Contaminated or undersized silencers increase backpressure and degrade both response time and vacuum system performance. Inspect and replace silencers on a scheduled maintenance interval.
• When installing solenoid pilot models in high-temperature environments, confirm that the solenoid ambient temperature does not exceed 180F (82C) even if media temperature reaches 300F. Physically separate the solenoid housing from direct thermal radiation paths using insulation or heat shields if necessary.
• For low-temperature installations below 0F (-18C), verify that Buna-N seals are specified and that the compressed air supply is dried to a dewpoint below the minimum operating temperature. Confirm that the solenoid coil insulation is rated for the application temperature range.
• Wire the 1/2" conduit connection using appropriate conduit fittings and wire gauges per local electrical code requirements. Confirm that the solenoid voltage matches the drive circuit output before energizing. Ground the solenoid housing through the conduit system or a dedicated ground wire in accordance with applicable electrical standards.
• Perform a functional test of the valve (using the manual override button if electrical power is not yet available) before connecting downstream actuators or applying full system pressure or vacuum, to confirm correct valve action and absence of leakage.
• After installation, cycle the valve several times at operating conditions and check all port connections, fittings, and pipe threads for leakage. In vacuum service, use a vacuum gauge on the downstream circuit to verify that the valve fully isolates vacuum when in the closed position.
• All service and maintenance operations must be performed only after shutting down the pneumatic and vacuum systems, exhausting all pressure, releasing all vacuum, and implementing lockout/tagout procedures per OSHA 1910.147 and EN 1037. Use only genuine ROSS replacement parts to maintain SIL certification integrity.

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 the purchase price at ROSS's discretion for products confirmed to be defective.

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

Global technical support is available through ROSS offices in the USA (headquarters in Ferndale, Michigan), Canada, Brazil, Germany, France, United Kingdom, India, China, and Japan. Regional engineering teams provide application support, valve selection assistance, and troubleshooting guidance.

Contact ROSS Controls USA at (800) 438-7677 or +1-248-764-1800, or visit rosscontrols.com for product configuration tools, technical documentation, CAD model downloads, distributor locator services, and direct engineering support.

Download Catalog: https://www.rosscontrols.com/en/documents/5341/21-series-valves