Size: 20, Backflow Function: None, Thread: Rc, Port Size: 1/4, Accessory: Set Nut for Panel Mount, Specifications: 1 + R, Pressure Unit: -

Regulator, Pressure Boosting Valve: Regulator, Regulator Type: Precision Control, Shape: Standard, Operating Environment: Standard, Compatible Fluid: Air, Exhaust Mechanism (Air Bleed): [Included] Bleed, Reverse Flow Function (Relief): No, Supply Side Connection Type: Rc, Supply Side, Connection Diameter: 1/4, Flow Direction: [Right] From Left to Right, Control Side Connection Type: Rc, Control

Regulator, Pressure Boosting Valve: Regulator, Regulator Type: Precision Control, Shape: Standard, Operating Environment: Standard, Compatible Fluid: Air, Exhaust Mechanism (Air Bleed): [Included] Bleed, Reverse Flow Function (Relief): No, Supply Side Connection Type: Rc, Supply Side, Connection Diameter: 1/4, Flow Direction: [Left] From Right to Left, Control Side Connection Type: Rc, Control

This is a legacy product, and replaced byARP30-02H

This is a legacy product, and replaced byAR25-02H-B

This is a legacy product, and replaced byAW40-02H-B

This is a legacy product, and replaced byAW30-02H-B

This is a legacy product, and replaced byAW20-02H-C-B

Size: 20, Backflow Function: K (Backflow Function), Thread: Rc, Port Size: 02 (1/4), Accessory: H (Set Nut for Panel Mount), Specifications: 3 (0.008 to 0.6 MPa Setting)

Regulator, Pressure Boosting Valve: Regulator, Regulator Type: Precision Control, Shape: Standard, Operating Environment: Standard, Compatible Fluid: Air, Exhaust Mechanism (Air Bleed): [Included] Bleed, Reverse Flow Function (Relief): [Included] Yes, Supply Side Connection Type: Rc, Supply Side, Connection Diameter: 1/4, Flow Direction: [Right] From Left to Right, Control Side Connection

This is a legacy product, and replaced byAR20K-02H-B, http://smcpneumatics.com/assets/images/pdf/ar.pdf

The ARP20/30/40 series is available with a back flow function that exhausts the air pressure in the outlet side reliably and quickly. 

Special Applications: 21- (Clean-room, Copper-free, Fluorine-free, Silicon-free), Size: 20, Backflow Function: K (Backflow Function), Thread: Rc, Port Size: 02 (1/4), Accessory: H (Set Nut for Panel Mount), Specifications: 3 (0.008 to 0.6 MPa Setting)

Special Applications: 10- (Clean Room Compliant), Size: 20, Backflow Function: K (Backflow Function), Thread: Rc, Port Size: 02 (1/4), Accessory: H (Set Nut for Panel Mount), Specifications: 3 (0.008 to 0.6 MPa Setting)

Special Applications: Clean-room, Copper-free, Fluorine-free, Silicon-free, Size: 20, Backflow Function: Backflow Function, Thread: Rc, Port Size: 1/4, Accessory: Set Nut for Panel Mount, Specifications: 0.008 to 0.6 MPa Setting, Pressure Unit: -

Special Applications: Clean Room Compliant, Size: 20, Backflow Function: Backflow Function, Thread: Rc, Port Size: 1/4, Accessory: Set Nut for Panel Mount, Specifications: 0.008 to 0.6 MPa Setting, Pressure Unit: -

Size: 20, Backflow Function: None, Thread: Rc, Port Size: 01 (1/8), Accessory: B (Bracket), Specifications: 3 (0.008 to 0.6 MPa Setting)

Size: 20, Backflow Function: None, Thread: Rc, Port Size: 02 (1/4), Accessory: BE (B+E), Specifications: 3 (0.008 to 0.6 MPa Setting)

Size: 20, Backflow Function: None, Thread: Rc, Port Size: 01 (1/8), Accessory: EH (E+H), Specifications: 3 (0.008 to 0.6 MPa Setting)

Size: 20, Backflow Function: None, Thread: Rc, Port Size: 02 (1/4), Accessory: BE4 (B+E4), Specifications: 3 (0.008 to 0.6 MPa Setting)