Relay Valve R-14H Horizontal Delivery and Supply Ports (2) 1/2in-14 Supply Ports (2) 1/2in-14 Delivery Ports (1) 1/4in-18 Service Port (1) 1/8in-27 Balance Port 4 psig Cracking Pressure Use w/ Bendix 296007 Mounting Bracket. Part number: EM36840 OE MFG: MACK OEM Reference: 745-104574 Cross Reference: OTHER : 745-104574 Product Class: Air Valves & Kits The PAI EM36840 is an R-14H relay valve with horizontal delivery and supply ports, identified by Mack reference 745-104574. Relay valves are heavy duty diesel truck parts that use a control signal to regulate compressed air delivery within a vehicle air-brake system. This valve has two 1/2in-14 supply ports, two 1/2in-14 delivery ports, one 1/4in-18 service port, one 1/8in-27 balance port, and 4 psig cracking pressure; it is specified for use with a Bendix 296007 mounting bracket.