Pulsafeeder PULSAtron Series A Plus chemical metering pumps are positive displacement, diaphragm type pumps. Output volume is adjustable while pumps are in operation from zero to maximum capacity. The PULSAtron Series A Plus guided check valves, with their state-of-the-art seat and ball designs, provide precise seating, and excellent priming and suction life characteristics. Out timing circuit is highly reliable and, by design, virtually unaffected by temperature, EMI and other electrical disturbances. Series A Plus pumps continue to meet their specifications for pressure and capacity even during extended use. That's because of our high quality solenoid and special enclosure that effectively dissipates heat. Agency Approved and water resistant for demanding outdoor and indoor applications.