Nilfisk-Advance MC 6P Service Manual page 32

Function
D
By-Pass valve system_MC 6P
13
8
12
9
9
2
3
10 11 10
5
7
1
6
4
14
By-pass valve function in high pressure running mode.
Motor is running, spray handle is open, water is flowing to the HP nozzle.
During operation there is high pressure at pos. 1,2,3,4,5,6. Water flows from the pressure valves (1)
through the injector nozzle (4) to the outlet (6) and out to the HP nozzle in the lance.
The pressure in the by-pass valve is higher above piston (10) than below. The reason for that is wa-
ter flowing through the injector nozzle. There is a pressure drop over the injector nozzle (restriction)
which means pressure is lost—on purpose, so we can control the position of the stem/lower piston.
(Higher pressure before injector nozzle than after) So the pressure in the channel/area (5) (below
lower piston (10)) is lower than in area (2, 3). The higher pressure above piston (10), will push down
the stem (11) against the seat (8), so water/pressure cannot escape between cone and seat—so all
water volume is flowing out to the HP nozzle in the lance. Piston (10) is also moving down, as lower
piston and stem is screwed together.
When the water regulator (13) is turned clockwise, the stem (11) and piston (10) will move up, and
the cone will lift from the seat (8) and some of the water volume will flow back to the pump water in-
let side. This means less water to the HP nozzle—equal lower pressure.
SM_MC_6P Ver.2.0_2021
32