Strainer for a bilge pump
A straining device for a drainage pump, the straining device comprising a body defining an inner chamber; at least one straining element by which liquid may enter the chamber; and at least one outlet by which liquid may leave the chamber. The straining device further includes a liquid level sensor arranged to detect the level of a liquid in which said straining device is located during use and, upon determining that said liquid level exceeds a threshold, to cause an activation signal to be sent to said pump. The liquid level sensor comprises non-contact sensing means such as an electric field sensor. The sensor is located at the top of the straining device and arranged to project its sensing field upwardly.
1. A straining device for a drainage pump, the straining device comprising a body having a roof and defining an inner chamber; at least one straining element by which liquid may enter the chamber; and at least one outlet by which liquid may leave the chamber, wherein the straining device further includes a liquid level sensor arranged to detect the level of a liquid in which said straining device is located during use and, upon determining that said liquid level exceeds a threshold, to cause an activation signal to be sent to said pump, and wherein said liquid level sensor comprises non-contact sensing means, wherein said liquid level sensor is located substantially at said roof and generates a directed sensing field in use, said liquid level sensor being positioned so that, in use, said directed sensing field extends substantially upwardly from said roof and substantially none of said directed sensing field extends below said threshold.
2. A straining device as claimed in claim 1 , wherein said liquid level sensor is located inside said chamber on an inner surface of said roof.
3. A straining device as claimed in claim 1 , wherein said liquid level sensor is located on an external surface of said roof, preferably located within a substantially liquid-tight cover.
4. A straining device as claimed in claim 1 , wherein said liquid level sensor is incorporated into the body.
5. A straining device as claimed in claim 1 , wherein said liquid level sensor includes at least one first liquid level sensing element that generates a sensing field in use, the arrangement being such that the sensing field extends only substantially upwardly in use.
6. A straining device as claimed in claim 1 , wherein the liquid level sensor is located at the roof, the arrangement being such that the sensing field extends generally upwardly from the roof in a direction substantially away from the body.
7. A straining device as claimed in claim 1 , wherein said liquid level sensor is arranged to cause said activation signal to be generated when the detected liquid level indicates that said at least one outlet is substantially covered by said liquid.
8. A straining device as claimed in claim 7 , wherein said at least one outlet is arranged such that its top edge is substantially at or below the level of the roof.
9. A straining device as claimed in claim 8 , wherein said at least one outlet is located in a side wall of said body.
10. A straining device as claimed in claim 1 , wherein said liquid level sensor is arranged to cause said activation signal to be generated when the detected liquid level indicates that said roof is substantially covered by said liquid.
11. A straining device as claimed in claim 1 , wherein said liquid level sensor comprises at least one electric field sensor or at least one other electromagnetic field sensor.
12. A straining device as claimed in claim 1 , wherein said liquid level sensor is arranged to cause a deactivation signal to be sent to the pump upon detecting that the liquid level has dropped below the threshold level, or a second threshold level.
13. A straining device as claimed in claim 12 , wherein the liquid level sensor is arranged to cause said deactivation signal to be sent only after absence of said liquid has been detected by said sensor at least twice within a threshold period of time.
14. A straining device as claimed in claim 12 , including at least one second liquid level sensing element that generates a sensing field in use, the arrangement being such that the sensing field extends substantially downwardly in use, said deactivation signal being dependent on the output of said at least one second liquid level sensing element.
15. A straining device as claimed in claim 14 , wherein said at least one second liquid level sensing element is arranged such that said second threshold level is substantially at the top of said outlet, said second threshold level being below, in use, said threshold level.
16. A straining device as claimed in claim 1 , wherein the liquid level sensor is arranged to continuously or intermittently cause the activation signal to be sent until it determines that the liquid level has dropped below the threshold level, at which time the activation signal is caused to terminate, termination of the activation signal being an indication that the pump is to be deactivated.
17. A straining device as claimed in claim 1 , wherein the liquid level sensor is arranged to cause the activation signal to be sent only after said liquid has been detected by said sensor at least twice within a threshold period of time.
18. A straining device as claimed in claim 1 wherein the liquid level sensor is arranged to cause said activation signal to be terminated only after absence of said liquid has been detected by said sensor at least twice within a threshold period of time.
19. A straining device as claimed in claim 1 , wherein said liquid level sensor is arranged such that said threshold level is substantially at the level of a top of said body or substantially at the level of the top of said outlet.
20. A pump system comprising a drainage pump with a pump control system and a straining device, the straining device comprising a body having a roof and defining an inner chamber; at least one straining element by which liquid may enter the chamber; and at least one outlet by which liquid may leave the chamber, wherein the straining device further includes a liquid level sensor arranged to detect the level of a liquid in which said straining device is located during use and, upon determining that said liquid level exceeds a threshold, to cause an activation signal to be sent to said pump control system, and wherein said liquid level sensor comprises non-contact sensing means, wherein said liquid level sensor is located substantially at said roof and generates a directed sensing field in use, said liquid level sensor being positioned so that, in use, said directed sensing field extends substantially upwardly from said roof and substantially none of said directed sensing field extends below said threshold.
21. The pump system of claim 20 , wherein said pump control system is configured to deactivate said pump in response to determining from said liquid level sensor that said liquid level does not exceed said threshold.
22. The pump system of claim 21 , wherein the control system is arranged to delay deactivation of the pump for a period of time after having received a deactivation signal from the sensor, or detected a termination of the activation signal, and, at the end of the delay period, to deactivate the pump only if an activation signal has not been received in the meantime.
23. The pump system of claim 20 , wherein said pump control system is arranged to delay activation of the pump for a period of time after having received an activation signal from the liquid level sensor and, at the end of the delay period, to activate the pump only if a deactivation signal has not been received in the meantime.
24. The pump system of claim 20 , wherein said pump control system is arranged to delay activation of the pump for a period of time after having received an activation signal from the liquid level sensor and, at the end of the delay period, to activate the pump only if the activation signal has not terminated in the meantime.