Two reservoir system in which fluid is drawn from one to maintain a level in the other

In a fluid system, a primary reservoir in which a liquid level is to be maintained, a sensor and pump adapted to draw fluid from said primary reservoir at said level and to produce a sensing signal when other than liquid is so drawn, a secondary reservoir, and pump means to transfer liquid from said secondary reservoir to said primary reservoir only in response to said sensing signal said sensor and pump having the capability of responding to the opposition of a fluid to its own physical displacement, and comprising:

• a body having a cavity therein, and flow conduit means enabling entry and exit of fluid to and from said cavity;
• a fluid displacement member which comprises a pump movable in order to vary the volume within said cavity which is available to be occupied by said fluid;
• force means adapted to give repetitively a known impetus to said fluid displacement member for the purpose of moving it repetitively to change said volume;
• and sensing means responsive to the motion developed by said member in response to said impetus, as such motion may vary with the varying opposition to said fluid to its own physical displacement by said member, to produce a signal respective to such opposition.

A liquid level control for a system which includes a primary reservoir in which a liquid level is to be maintained and a secondary reservoir containing reserve liquid to be added when the said level is low, said control comprising:

• first pumping means for withdrawing liquid from said primary reservoir and delivering it to said secondary reservoir;
• a sensor adapted to withdraw fluid from said primary reservoir at said liquid level and to produce a sensing signal when other than liquid is so withdrawn;
• and a second pumping means adapted to transfer liquid from said secondary to said primary reservoir in response to said sensing signal;
• whereby liquid may be withdrawn from said primary reservoir when said level is high, thereby to reduce said level, and whereby liquid may be withdrawn from said secondary reservoir and transferred to said primary reservoir when said level is low, said sensor having the capability of responding to the opposition of a fluid to its own physical displacement, comprising:
• a body having a cavity therein, and flow conduit means enabling entry and exit of fluid to and from said cavity;
• a fluid displacement member movable in order to vary the volume within said cavity which is available to be occupied by said fluid;
• force means adapted to give repetitively a known impetus to said fluid displacement member for the purpose of moving it repetitively to change said volume;
• and sensing means responsive to the motion developed by said member in response to said impetus, as such motion may vary with the varying opposition of said fluid to its own physical displacement by said member, to produce a signal respective to such opposition.

In combination:

• a primary reservoir for containing liquid at a selected level;
• a secondary reservoir containing reserve liquid;
• a first and a second pump, said first pump being adapted to withdraw fluid from said first reservoir at said level and to discharge into said secondary reservoir, said second pump being adapted to withdraw liquid from said secondary reservoir and to discharge into said primary reservoir;
• sensing means to detect gas or vapor when withdrawn in substantial amounts by said first pump from said primary reservoir;
• and
• circuit means for causing said second pump to operate when gas or vapor is detected by said sensing means, but to discontinue such operation when only liquid is detected by said sensing means.