ALTITUDE vs PERFORMANCE (ATMOSPHERIC LOSSES)
Engine performance DECREASES with altitude. The higher the altitude, the less air there is available to support combustion. Maximum engine power DECREASES about 3.5% per 1000 feet of altitude.
Less air also means there is less air pressure to push on the body of water we are trying to draw into the pump. Because there is less air pressure forcing the water into the pump, the maximum available suction head is DECREASED. The reduction in engine power may also result in a reduced discharge capacity.

Pumps