Burkert Type 8715 - Manual (Page 10)

10
Descriptionofthesystem
Type 8700, 8701, 8703, 8705
Zero point shut-off
A zero point shut-off is integrated to ensure the sealing function of the
valve. This is activated if the following conditions occur at the same time:
Set-point value < 2 % of
nominal flow-rate Q
nom
(with control range 1:50)
and
Measured value < 2 % of
nominal flow-rate Q
nom
(with
control range 1:50)
If the zero point shut-off is active, the PWM signal is set to
0 % so that the valve is completely closed.
5.3.2. mfc solenoid valve
The solenoid valve used for an MFC is a direct-acting, normally closed
solenoid control valve.
The ND (nominal diameter) of the solenoid control valve is determined
by the required nominal flow-rate Q
nom
, the pressure conditions in the
process and the density of the operating fluid.
If the device is operated within the specified pressure range,
the solenoid valve also takes over the sealing function
together with the control function. Limitation: in the case
of special, hard seal materials, the seal function cannot be
ensured. In this case an additional shut-off valve may be
required.
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