Page 165 - Physics

Pressure

The handle operates a reciprocating The process is repeated; hence, it is continuous.
mechanism that raises and lowers Atmospheric pressure can support a water column
a piston with a transfer valve at its of about 10 m. This means that the pump cannot be
centre. The piston acts to separate higher than 10 m above the water level.
the pump cylinder into upper and
lower chambers and the transfer Task 7.6
valve controls the fl ow of water
between them. At the bottom of Using online and other sources discuss the main
the lower chamber is an intake features, mode of operation and limitations of
valve that controls the fl ow of a lift pump. What are the uses of a lift pump in
your daily life?
water from the external source.
The pump starts with the piston at
the bottom of the empty cylinder Force pump
and both valves closed.
A force pump is a modifi cation of a lift pump. It

The pump handle is then pushed consists of a cylinder fi tted with a solid piston, as
down lifting the piston upwards. shown in Figure 7.36. There are intake (B) and
The transfer valve remains closed output valves (A). The piston is moved up and down
and the intake valve opens to allow by a motor or by hand. When the piston moves up,
water from the external source to the intake valve opens and the output valve closes
fi ll the lower chamber. This is due due to the low pressure created between the piston
to the low-pressure region created and the intake valve. This draws water from the
between the transfer valve and the external source into the pump cylinder. When the
piston. piston moves down, the intake valve closes and
the output valve opens; this forces the water in the
The handle is lifted upwards cylinder to go out of the pump.
pushing the piston down. The Up
intake valve closes and the transfer Down
valve opens allowing water to pass Piston
into the upper chamber.
Pump B A
The pump handle is pushed down cylinder
again lifting the piston upward.
The transfer valve closes and the
intake valve opens to allow water
from the external source to fi ll the
lower chamber. The water in the Figure 7.36: Force pump
upper chamber is lifted and fl ows A force pump moves water from deeper depths
out of the spout. than the lift pump.

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