Double Acting Reciprocating Pump

Reciprocating pump is a positive displacement pump(say true or false)
A reciprocating pump is suitable for less discharge and higher heads. (Say true or false)
Is priming required for reciprocating pump?( Say Yes/ No)
In a reciprocating pump, air vessels are used to
The relation between hydraulic efficiency ηh, mechanical efficiency ηm and overall efficiency ηo is