Data Sheet for Product

Siemens Building Technologies CA1N4028 / 11.1998
Landis & Staefa Division 5/12
Relationship between stroke and flow rate
The construction of the valve with a flexible disc as the control element
means that a minimum flow is obtained immediately, as soon as the valve is
“cracked” open. With an increasing positioning signal, the valve opening
increases in proportion to the stroke, producing a linear increase in flow (see
Fig. 11).
This flow characteristic applies both to control path 1 → 3 and to control
path 2 → 3. When the valve is used for mixing, the two flows combine to
give a constant flow value.
• Overcoming the pressure forces
Differing pressures across the control path affect the magnetic force, but
this potential problem can be virtually eliminated through pressure
balancing. This ensures that the magnetic force is primarily used for flow
control. Pressure balancing is an extremely effective solution and is achieved
in practice with the aid of a bellows (Fig.10). Pressure p
2
passes through a
passage in the stem into the inside of the bellows and equalises the pressure
p
2
acting on the lower side of the valve disc. Pressure p
1
, working on the
upper side of the disc, is equalised by the pressure p
1
acting on the lower
side of the bellows. This solution, within the valve itself, involves neither a
special compensatory circuit nor any additional space.
Fig. 10: Pressure balancing
94.0410
100
[%]
H
H
100
[%]
k
v
k
vs
100
Fig. 11: Flow characteristic