Product:  ARO hoist valves

Models: 7700- E and ET Series Chain Hoist

Subject: ARO 7700 Hoist Series O-Ring Change

By: Tom Gagnet, Marketing Manager
        Industrial Lifting Equipment

No. UL-021

Date: 9/12/02

ARO 7700 Hoist Series O-Ring Change

Circular Letter No. MHD-488      click here to view as a PDF
The O-Ring material on ARO hoist valves has been changed from nitrile to polyurethane. Please reference the attached illustrations for the exact location and part numbers of the two O-Ring’s that have changed. This change has already been made on production hoist some time ago. The purpose of this UpLink is to insure that the proper O-Rings are selected and installed during service and repair. The new O-Rings can be easily identified by the color. The new polyurethane material is yellow and has a higher durometer hardness. The O-Ring material was changed is to improve the durability of the brass valve bushing that they seal. These O-rings seal the hoist inlet air from the motor at the the end of the brass bushing containing the geared spool valve. Should the O-Ring be cut and lost, the hoist will continue to operate but will allow the adjoining metal valves, at either end, to impact the brass bushing, deforming the metal each time the hoist is operated. If you have experienced the geared spool valve being free in the middle of the brass bushing, but required to be driven out of the end to be removed, it is most likely the result of the bushing being deformed by repeated impact after the O-Ring was lost or deformed. The new yellow polyurethane material offers superior abrasion resistance, shock load capability and tensile strength greatly increase durability. It is most important that the subject O-Rings be replaced druing any repair with the new stronger material to take advantage of the increased service life of the valve chest components.
Return  to Index