Fuel Feed Pump - Yanmar 4LHA-HTP Operation Manual

Chapter 3 Fuel Injection Equipment

6. Fuel Feed Pump

6. Fuel Feed Pump
6-1 Fuel Feed Pump Design and Function
The fuel feed pump consists of a priming pump, which
extracts air from the fuel system and is used manually
to feed fuel while the e n g i n e is stopped, and a feed
pump, which supplies fuel while the engine is running.
The fuel feed pump is d r i v e n by an eccentric cam on
the fuel camshaft.
When the cam pushes on t h e piston via the roller guide,
the fuel in the piston c h a m b e r passes through the dis-
Holder
P W M L Piston spring
M ^ X a s k e t
Plug
3-2-40
charge valve and flows behind the piston. The suction
valve closes under pressure and prevents the fuel from
flowing back to the tank.
When the cam is lowered, the piston is pushed back by
the piston spring and the fuel behind the piston
chamber is forced to the fuel pump. The negative pres-
sure which develops in the piston chamber makes the
suction valve open and fills the piston chamber with
fuel.
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4LHA Series