The push buttons on a Hubbell Industrial Controls explosion-proof hoist pendant control can become so stiff that they will not return at all, according to the US Navy Crane Centre.
On the XPBC remote, a stainless steel pushbutton shaft moves through a hole in an aluminium pendant plate. As the two dissimilar metals corrode, the shaft’s resistance to movement increases to the point where the button will not spring back to its original position, or spring back only slowly.
The Navy recommends that corroded hoist controls should be fitted with optional bronze bushings to help prevent future corrosion. The Navy issued an ‘equipment deficiency memorandum’ on the problem in its March 2005 Crane Corner newsletter.
In an unrelated incident, the Navy reported that a crane operator was raising a load by pressing the ‘up’ button on an unspecified remote control. When he released the button, the hook continued to rise. After investigating, technicians discovered that someone had installed a contactor that was undersized for the hoist motor, which caused the contacts to weld closed.
