Grundfos DMH 28X Installationsanleitung Seite 12

5. Product description and accessories
5.1 General description
The DMH 28X are positive-displacement pumps with hydraulic
diaphragm control. The operation procedure of the dosing pump
is shown in the sectional drawing. See figs
The rotational movement of the motor (1p) is converted via the
worm gear (2p) and eccentric (3p) into the reciprocating
movement of the piston (6p). The piston has a hollow bore and a
row of radial control holes, which provide a hydraulic connection
between the drive area and the piston stroke area. The sliding
sleeve (5p) covers the control holes during the stroke and seals
the stroke area from the drive area.
V 3b E
3a 2 Q
Fig. 2 DMH 280
V 3b E M
3a 2 Q 9p
Fig. 3 DMH 281
12
2 to 6.
M


9p 6p 5p 2p 3p


6p 5p 2p 3p
The hydraulic-driven movement of the PTFE diaphragm (Q)
displaces an equivalent volume of dosing medium from the
dosing head (2) into the dosing line. With the suction stroke, the
piston creates a low pressure, which is established in the dosing
head. The ball valve (3b) on the dosing side closes and the
dosing medium flows through the suction valve (3a) into the
dosing head.
The stroke volume size is determined by the position of the
sliding sleeve. The active stroke length and corresponding
average dosing flow can be changed continuously and linearly
from 10 % to 100 % using the stroke-length adjustment knob and
Vernier scale (L).
1p
F
L
1p
F
L