IM-P402-84 AB Issue 6
2
Your attention is drawn to Safety Information Leaflet IM-GCM-10.
1. Safety
2. Application
When a large steam demand is made of a boiler,
the pressure will drop, and large bubbles of
steam will be formed in the water. This causes
the water level to rise, and can cause the
feedwater valve to close. Although the level of
water has increased, the mass of water will be
decreasing, a situation which actually
requires the feedwater valve to be opening. A
two element control system (probe / level
controller and steam flowmeter), uses the
output from the steam flowmeter to move the
set point of the level controller.
This compensates for the tendency of the
feedwater valve to close when the steam
demand is high. Under certain conditions
where the boiler feedwater pressure varies
considerably, perhaps due to other boilers
drawing water, three element control provides
even closer compensation.
A three element control system uses an
additional input from a water flowmeter to
compensate for any variations in feedwater
pressure.
3. Description
The Spirax Sarco LC2400 is used to connect
a level controller to the 4 - 20 mA output signals
from the steam flowmeter and (where fitted),
the water flowmeter. The controller can be an
LC2200 (for an electrically actuated feed valve),
or an LC2300 (for a pneumatically actuated
valve). The LC2400 has 'steam' and 'water'
potentiometers which are used to scale the
outputs of the meters. A green LED next to each
potentiometer indicates that a signal is present.
4. Installation
Warning
Isolate the mains supply before unplugging
LC2200 or LC2300 controllers since live
terminals at mains voltage will be exposed
in the controller base.
Controllers should be installed in an enclosure
or control panel to provide environmental
protection.
CAUTION:
Allow 15 mm spacing between
adjacent units for air circulation.
Spirax Sarco can provide suitable enclosures.
The controller may be mounted on a 'top hat'
section DIN rail using the mounting clip
provided, or the clip may be removed and the
controller base screwed direct to a chassis
plate.