This pump is designed to transfer water from a fresh water tank to a waterbox. Its simple design bypasses internally and it does not require a pressure switch or an expansion tank.
 
550 Series 12VDC 4.0 GPM
Features:
By-pass 50 PSI
4.2 GPM 
12 VDC 15.0 amps 
Inline 15 amp Fuse
3/4" FPT Female ports
5 Chamber
QTS556 Fittings