By-Pass Valve
The by-pass valve allows fluid to fill the drill string while tripping in the
hole and to drain while tripping out. When mud is pumped, the valve closes
causing fluid to move through the tool. Most valves are of a spring piston
type which closes under pressure to seal off ports to the annulus. When
there is no downward pressure, the spring forces the piston up so fluid can
channel through the ports to the annulus. (Figure 5-20).
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