FUEL OIL PUMP

         


           

BOSCH  PUMP :

          The principle operation  of port controlled fuel pump . The main advantage of this type of pump elimination of valves which automatically makes the pump free from valve – related problems . The type of pump is simple & has an advantage over the other types on the point of reliability it is an obvious choice for  all small engines .

          It consist of a plunger closely fitted inside a barrel . The  forward stroke of the plunger is filling period which the pump barrel is filled up  through a suction port which is connected to a chamber surrounding the barrel .During the upward stroke of the plunger a pressure is crated immediately after the inlet port is covered .The delivery takes place by lifting a spring loaded delivery valve fitted above  the pump chamber .

          The regulation of the quantity of the fuel is effected by grooves

in the plunger . The plunger is capable of rotation about its

longitudinal axis besides   a vertical oscillatory motion . It has on

its body a vertical slot & a milled helix .When the plunger 

angular position is such that the vertical  sot is held against  the                                      

the suction port  the pumping of the plunger creates no pressure in

the pump barrel .When the plunger is turned away from this position

it is set for admission of fuel . A pressure  is created in the  space

above  the plunger as soon as the suction ports are covered . The

injection begins almost  instantaneously & is continued till the

helical edge uncovers  the suction port . the pump may b se at

any intermediate  position between no delivery to maximum delivery.

The top edge  of the plunger controls the beginning of the injection

Which  once set remains constant during the operation of the engine .

The end of injection is controlled bye the profile of the helical edge

which  variable . When the helical edge uncovers the suction port 

the pressure in the pump chamber is quickly decayed  terminating

the delivery .For  the fuel regulation  the plunger is turned away

to another angular position . The angular position of the plunger in

relation to the suction port determines the quantity of fuel delivery

 The action of the pump is further explained with reference to

 The plunger is set for a certain control position .

1.     The plunger is in its lowest position . The pump barrel is being filled up with oil under  pressure (gravity or low pressure pump )

2.     the plunger performs the pumping stroke  . At a certain specified(and adjusted)time  its\ covers the inlet port The effective delivery of the fuel starts from this very moment  as the pressure rises instantly the liquid being  almost incompressible.  The pressure overcomes the delivery valve & the injector needle  valve spring pressure .

3.     then injection is continued till at the very moment the helical edge uncovers the suction port & the space above the plunger is communicated to the suction chamber . Sudden  loss of pressure causes  the needle valve & the delivery valve to be  seated instantly terminating the delivery .

4.     The plunger is rotated & set  to another  position  . It will  be seen that  the suction port  is covered by the upper edge of the plunger at the time . Hence the beginning of injection remains at the same time in the cycle .

5.     The termination delivery is effected earlier by the helical control edge coming into action earlier resulting in a shorter effective stroke of   the plunger .

6.     The plunger is further rotated so that the space above the plunger is always communicated during the full travel of the plunger this the zero admission point as there can be no delivery by the pump.