Abstract Liquid developer is piped through a metering device to which the liquid flows by gravity from a reservoir. The open lower end of a vertical air pipe extends downwardly into such reservoir, terminating at the normal level of the liquid therein. Liquid is supplied to the reservoir from a liquid supply container through a conduit containing a pump which elevates the liquid from the bottom of the container to the top of the reservoir. An overflow outlet in the side of the reservoir returns any liquid rising above such normal level back to the container by gravity. The upper end of the air pipe is in closed air communication with an air pressure sensitive switch and a source of air, under pressure, preferably the blower, or air exhaust of the machine. Thus, should the liquid level in the reservoir fall below the vertical air pipe, air flows out of the pipe, and thereby lowers the air pressure effectively acting on the switch. This, in turn, operates a fail-safe relay, and the latter closes contacts to apply electrical current to a suitable signal device, such as a lamp, buzzer, indicating the low status of the liquid developer in the system.
A liquid supply indicator for the liquid developer supply system of whiteprint duplicating machines, comprising: a metering device for supplying liquid to a developer; a liquid reservoir for feeding liquid by gravity to said device; a liquid supply container located below said reservoir; means including a liquid pump for conveying liquid from the bottom of said container to the top of said reservoir; a low liquid level indicator; an air pressure sensitive switch; and means including an air pressure supply for applying a small amount of air under very low pressure in parallel to said switch and to a selected level of the liquid in said reservoir which is open to the atmosphere, whereby in case such selected level falls therebelow, such air under pressure is vented, causing the air pressure applied to said switch to drop, operating the switch, and energizing the indicator, thereby indicating such low level condition of the liquid in the reservoir.
Claim 2
Dependent Claim
156 words
A liquid supply indicator for the liquid developer supply system of whiteprint duplicating machines, comprising: a metering device for supplying liquid to a developer; a liquid reservoir for feeding liquid by gravity to said device; a liquid supply container located below said reservoir; means including a liquid pump for conveying liquid from the bottom of said container to the top of said reservoir; a low liquid level indicator; an air pressure sensitive switch; and means including an air pressure supply for applying a small amount of air under very low pressure in parallel to said switch and to a selected level of the liquid in said reservoir which is open to the atmosphere, whereby in case such selected level falls therebelow, such air under pressure is vented, causing the air pressure applied to said switch to drop, operating the switch, and energizing the indicator, thereby indicating such low level condition of the liquid in the reservoir.
Claim 3
Dependent Claim
87 words
The invention as defined by claim 1, wherein: the air pressure sensitive switch includes a diaphragm comprising a wall of a closed chamber that is in closed air communication with a vertical pipe the lower end of which normally is closed by the level of the liquid in said reservoir, so that the normal air pressure is sufficient in the chamber to keep said switch closed, and fail-safe relay means operative upon the opening of said switch to connect said indicator to a source of electrical power.
Claim 4
Dependent Claim
17 words
The invention as defined by claim 2, wherein: the air pressure supply comprises the machine air exhaust.