Product Description And Accessories; General Description - Grundfos DMH 28 Serie Montage- Und Betriebsanleitung

5. Product description and accessories

5.1 General description

The DMH 28X are oscillatory 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 drive motor (1p) is converted via
the worm gearing (2p) and eccentric (3p) into the oscillatory
suction and stroke 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 plug (5p) envelops the 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
2 to 6.
M


9p 6p 5p 2p 3p


6p 5p 2p 3p
The hydraulic excursion of the solid PTFE diaphragm (Q)
displaces an equivalent volume of dosing medium from the
dosing head (2) into the discharge line. With the suction stroke,
the piston creates a low pressure, which propagates 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 solely determined by the position of the
sliding plug. The active stroke length and corresponding average
dosing flow can therefore be changed continuously and linearly
from 10 % to 100 % using the stroke-length adjustment knob and
Nonius (L).
1p
F
L
1p
F
L
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