Emerson 2468CD Manuel D’Utilisation

Hydrastep Pressure Parts 

General Introduction 

The Hydrastep systems have been designed as electronic alternatives to conventional visual 
water gauges on boilers, giving more reliable and safer water level indication. 

The system is based on the significant differences in resistivities of water and steam over 
the range 100

C (212F) to 370C (698F).  (Series 3 super-critical components are used up 

to 560

C, 1040F) 

A vertical row of electrodes is installed in the water column which forms a side arm attached 
to a boiler arid aligned, typically, such that an equal number of electrodes appear above and 
below the normal water level, see Figure 1.1.  The resistance measurement is made 
between the insulated tip of the electrode and the wall of the column.  The cell constant, 
defining the actual resistance measured, is determined by the length and the diameter of the 
electrode tip and the water column bore.  In practice, the cell constant is chosen so that the 
resistance in water is less than 100k ohms, with a consequent resistance in steam of greater 
than 10M ohms. 

Since the resistivities of water and steam are substantially different, the system is simple 
and requires minimum setting up adjustments.  It is not critical in terms of power supply 
variations, ambient temperature changes, etc., resulting in a highly reliable system. 

Figure 1.1 shows the resistance-measuring cell complete with installed electrode. Figure 1.2 
and Figure 1.3 show examples of the Low Pressure (120bar, 1740p.s.i.) and the Series 3 
and Super 3 High Pressure (210bar, 3045p.s.i. & 300bar, 4350p.s.i.) Water Columns 
respectively. 

Each electrode is connected to its own electronic measurement channel where the 
resistance value measured decides which of two Light Emitting Diode (LED) drive circuits is 
energised.  The LEDs are presented in two columns, one column of green LEDs (illuminated 
for water) and one column of red LEDs (illuminated for steam) indicating the water level.