to prevent surge
If only one spring were used on each valve, the valve would surge and bounce because of the natural vibration frequency of the spring.
damber valve
A valve spring "keeper" or AKA a valve spring "retainer" is used to lock a valve spring to the valve.
the discharge service valve is closed.
Valve pocketing is when a valve is hammering the valve seat.mostly due to miss adjusted valve spring/wrong valve spring/to strong of a valve spring or valve stem to short.Makes the valve seat deeper.
High performance piston aircraft engines do have valve overlap, just like high performance engines used in land vehicles, and for the same reasons. Listen to the Continental O-470, IO-520, IO-550, even IO-360 at idle (or Lycoming IO-540) and you can hear the same exhaust note quality as a racing car engine.
A food valve is not essential in a reciprocating pump because these pumps are designed to create a pressure differential that allows fluid to flow without the need for a valve to control the inlet or outlet. The reciprocating action of the pump's piston or diaphragm effectively manages the flow, preventing backflow and ensuring consistent delivery of fluid. Additionally, the pump's design inherently accommodates the necessary sealing and pressure retention, making a food valve redundant for its operation.
how many positions does a spring offset valve have
you need to compress the spring with a valve spring compressor tool, and then remove the valve keepers, and retainer.
The valve spring is the spring that closes the valve in the engine head after the cam lobe or rocker opens it . If the valve didn't close, many things would happen , the main one being the motor would not fire .
The purpose of the valve spring is to maintain contact between the components in the valve train, so the valve motion will follow the cam profile.
Your engine will probably missfire and you will not have compression in the cylinder that has the broken valve spring because your valve will stay open.