Pressure switch actuator

A motor control circuit for the comminuter motor of a waste disposal unit, incorporating an air sack around the inlet to the waste disposal unit, and a pressure responsive electrical switch, the motor being de-energized in absence of a pressure signal from the sack caused by the insertion of a safety guard in the inlet.

This invention is concerned with the control of electric motors in wet or 
damp environments, and is particularly concerned with waste disposal 
apparatus. 
While the invention will be described in relation to waste disposal 
apparatus, it will be understood that the invention has wider 
applications. 
With domestic waste disposal apparatus it is clearly dangerous to allow 
operation while there is unrestricted access to the comminuter of the 
waste disposal apparatus. It is therefore desirable to provide a guard on 
the inlet to the comminuter, the guard operating a control switch in the 
comminuter motor control circuit to allow or cause energisation of the 
motor. 
It is an object of the present invention to provide such a guard operated 
switch arrangement that is not adversely affected by the wet environment 
of the guard. 
The present invention is a motor control circuit incorporating a pressure 
operated switch, a flexible air sack communicating with the switch, and a 
member locatable to act upon the sack to increase the pressure therein and 
thereby operate the switch. 
Preferably the air sack and the member are annular. 
The air sack may be located around the access opening to a waste disposal 
comminuter and the member may be a guard member. 
The present invention is also a sink outlet pipe having a flexible air sack 
secured thereto, a removable guard member being located in the outlet to 
act upon the sack to reduce the volume thereof. 
Preferably the sack is annular and is secured round the internal wall of 
the pipe. 
A cover may be provided to protect the sack.

Referring now to the drawings, a sink outlet pipe 10 is supported by an 
external flange 11 on a dished ring 12 surrounding the opening in the 
bottom 13 of a sink. The outlet pipe 10 provides communication between the 
sink and waste disposal apparatus (not illustrated) which incorporates a 
comminuter driven by an electric motor. 
The pipe 10 has at its lower end an internal flange 15 on which is 
supported a flexible air sack 16 which is annular and is located against 
the interior surface of the pipe. An outlet pipe 17 leads from the sack 16 
through the wall of the pipe 10. A cover 18 is provided over the air sack 
16 to protect it against mechanical damage. 
A number, in this embodiment four, spaced axially extending openings 20 are 
provided in the cover 18 to co-operate with axially extending keys 21 on 
the periphery of a guard member 22 which is removably mounted on the cover 
18. When the member 22 is in position on the cover 18, as seen in FIG. 2, 
the keys 21 pass through the openings 20 and engage the sack 16 to reduce 
its volume. The guard member 22 acts to restrict access from the sink to 
the space below the pipe 10 in which the comminuter operates. 
The outlet pipe 17 is connected by a capillary tube 25 to a pressure 
operated switch 26 (see FIG. 2) in the supply circuit to the motor driving 
the comminuter. 
Considering now the operation of the embodiment described. In the absence 
of the guard member 22 access to the comminuter is unrestricted and, for 
example, a person's fingers could be inserted into the comminuter space. 
However the pressure operated switch 26 in the motor supply circuit is 
open thus preventing energisation of the comminuter motor so that there is 
no danger. To close the pressure operated switch 26 thus causing or at 
least permitting energisation of the motor it is necessary to insert the 
guard member 22 to cause its keys to act upon the sack 16 to increase the 
pressure therein, the increased pressure being of course transmitted to 
the pressure operated switch 26 by the tube 25. When the guard member is 
in position, of course, a person's fingers cannot be inserted into the 
comminuter space. 
The embodiment described thus has desirable safety features while avoiding 
problems associated with electrical switches in the wet environment of the 
guard member.