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5 Functional description

5.1

Pump

The metering pump is an oscillating diaphragm pump, the stroke length of

which is adjustable. An electric motor drives the pump.

5.2 Liquid end

The diaphragm (2) hermetically shuts off the pump volume of the dosing

head (4) towards the outside. The suction valve (1) closes as soon as the

diaphragm (2) is moved in to the dosing head (4) and the feed chemical

flows through the discharge valve (3) out of the dosing head. The dis‐

charge valve (3) closes as soon as the diaphragm (2) is moved in the

opposite direction due to the vacuum pressure in the dosing head and

fresh feed chemical flows through the suction valve (1) into the dosing

head. One cycle is thus completed.

Fig. 7: Cross-section through the liquid end

1 Suction valve

2 Diaphragm

3 Discharge valve

4 Dosing head

5 Backplate

13 Safety diaphragm

5.3 Integral relief valve

The integral relief valve normally operates as a simple, directly controlled

bleeder valve. The feed chemical then flows out through the hose connec‐

tion, e.g. into a storage tank, as soon as the pressure exceeds the pre-set

pressure value.

The integral relief valve can only protect the motor and the gear, and then

only against impermissible positive pressure that is caused by the

metering pump itself. It cannot protect the system against positive pres‐

sure.

The integral relief valve works as a bleed valve if the rotary dial is turned

clockwise up to the "open" stop, acting as a priming aid when starting up

the pump against pressure.

Functional description

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Sigma S2Ba Betriebsanleitung Seite 14