ARO 637421 Air Section Service Kit, Santoprene, 2 and 3 in. EXP

The ARO 637421 is the air section service kit for EXP Series diaphragm pumps in the 2 in. and 3 in. sizes, and its listed material is Santoprene. It works on the pneumatic side of the pump, the air motor that shifts the diaphragms, not on the wetted fluid parts.

ARO service documentation describes the kit as covering track and air-motor gaskets, Nitrile O-rings, U-cup seals, a pilot piston assembly, two 94102 Santoprene check diaphragms and service grease. The pilot piston and its seals control how the main air valve switches from stroke to stroke.

When to Use This Kit

• Internal air leakage across the air motor seals
• Irregular cycling, or a pump that stalls partway through a stroke
• Pilot valve wear found during planned air-motor maintenance

This kit does not cover the fluid section. If diaphragms, balls or seats also need attention, order the matching fluid-section kit as well.

Fits These ARO Pumps

The parts lists of 124 ARO pumps include the 637421. Examples:

• ARO PD30A-AAP-AAA-C
• ARO PD30S-ASS-SAA-C
• ARO PD30S-FSS-STT-C
• ARO PD30A-AAS-FGG-C
• ARO PD30A-AAS-FVV-C
• ARO PD20A-AAP-AAA-B
• ARO PD30A-AAP-KVV-C
• ARO PD30A-ACP-GGG-C

Those eight are shown here, and 116 more pump models list it too.