Additional equipment
34
Bourdon tube, capsule, diaphragm, spring diaphragm pressure gauges
9.3
Siphons
If the temperature of the measured fluid at the measuring point is
higher than the permissible operating temperature of the pressure
gauge, the shut-off units and the pressure gauges must be protected
from the hot fluid by means of sufficiently long measuring lines or si-
phons. Siphons (see current AFRISO catalogue or www.afriso.com)
help to condense the fluid for the elastic measuring element and help
to protect the pressure gauge from excessive temperatures of the
measured fluid.
1.
Mount a siphon filled with the fluid or a similar device close to
the pressure gauge and fill it with the condensate of the fluid.
2.
Pressurise the arrangement.
The hot measured fluid cannot reach the measuring device
when pressure is applied.
9.4
Chemical seals
If the fluid is corrosive, hot, highly viscous or crystallising, chemical
seals may be used to help prevent the fluid from reaching the pres-
sure gauge. A neutral liquid is used to transmit the pressure to the
measuring element.
1.
Select this pressure transmission liquid according to the meas-
uring range, temperature, viscosity, compatibility of the liquid
and the fluid to be measured and other factors.
2.
The installation of a cooling element between chemical seal and
pressure gauge is advised so that the pressure transfer liquid
can withstand the temperature of the fluid.
3.
Do not separate the connection between chemical seal and
pressure gauge.
Diaphragm pressure gauges offer an alternative to Bourdon tube
pressure gauges with chemical seals. The accuracy class infor-
mation shown on the dial applies to an ambient temperature of
+20 °C. According to EN 837-1 a deviation resulting from tempera-
ture influences of up to 0.08 %/K of the full scale value is permissible
for diaphragm pressure gauges.
9.5
Overpressure safety devices
If, for operational reasons, the range must be smaller than the
maximum operating pressure, install an upstream overpressure
safety device to help protect the pressure gauge from damage.
Highly viscous or polluted media may have an adverse effect on the
operation of the overpressure safety device or can render it ineffec-
tive.
