Yokogawa EJA220A - Manual (Page 23)

IM 01C21C01-01E 5-1
5. INSTALLING IMPULSE PIPING
5. INSTALLING IMPULSE PIPING
5.1 Impulse Piping Installation
Precautions
The impulse piping that connects the process outputs to
the transmitter must convey the process pressure
accurately. If, for example, gas collects in a liquid-
filled impulse piping, or the drain of a gas-filled
impulse piping becomes plugged, the impulse piping
will not convey the pressure accurately. Since this will
cause errors in the measurement output, select the
proper piping method for the process fluid (gas, liquid,
or steam). Pay careful attention to the following points
when routing the impulse piping and connecting the
impulse piping to the transmitter.
5.1.1 Connecting Impulse Piping to the
Transmitter
(1) Check the High and Low Pressure Connec-
tions on the Transmitter (Figure 5.1)
Symbols “H” and “L” are shown on a capsule assem-
bly to indicate high and low pressure side. For liquid
level measurement in an open tank, the ‘L’ (low
pressure) side is used to refer atmosphere. For a
closed tank, connect the impulse line to the low
pressure side of the transmitter. This will refer the
pressure in the tank.
“ H ” and “ L ” are shown
Low pressure
connection
Process connector
Bolt
F0501.EPS
Figure 5.1 “H” and “L” Symbols on a Capsule Assembly
(2) Tightening the Process Connector Mount-
ing Bolts
After connecting the impulse piping, tighten the
process connector mounting bolts uniformly.
(3) Removing the Impulse Piping Connecting
Port Dustproof Cap
The impulse piping connecting port of the transmitter
is covered with a plastic cap to exclude dust. This cap
must be removed before connecting the piping. (Be
careful not to damage the threads when removing this
cap. Never insert a screwdriver or other tool between
the cap and port threads to remove the cap.)
5.1.2 Routing the Impulse Piping
(1) Impulse Piping Slope
The impulse piping must be routed with only an
upward or downward slope. Even for horizontal
routing, the impulse piping should have a slope of at
least 1/10 to prevent condensate (or gases) from
accumulating in the pipes.
(2) Preventing Freezing
If there is any risk that the process fluid in the impulse
piping or transmitter could freeze, use a steam jacket or
heater to maintain the temperature of the fluid.
NOTE
After completing the connections, close the valves
on the process pressure taps (
main valves), the
valves at the transmitter ( stop valves), and the
impulse piping drain valves, so that condensate,
sediment, dust and other extraneous material
cannot enter the impulse piping.