Xterminator Dynamic Balancing
The Marflow Xterminator is also offered with dynamic flow control valves both as fixed flow rate limiters for use in 4 port control systems and as pressure independent control valves with integral 2 port temperature control valves.
By using dynamic flow control valves with internal pressure regulators a constant flow rate can be maintained at the terminal unit without the need for external pressure regulation and large diameter sub-mains balancing valves.
This not only improves flow control but leads to a reduced capital outlay and system commissioning cost. The Marflow Xterminator is offered with an externally adjustable automatic balancing valve for use in constant volume systems. A pressure independent control valve (PICV) is offered for variable volume systems.
In addition to providing maximum flow rate limitation the PICV includes a 2 port temperature control valve. By virtue of the internal pressure regulation the authority of this 2 port valve is very close to 1.
How Dynamic Balancing Valves Function
Dynamic balancing valves function using an internal diaphragm that acts against a spring to maintain a constant differential pressure across a fixed orifice thereby maintaining a fixed flow rate.
The figure right (Fig 1) illustrates a cross section of a typical automatic balancing valve.
In a pressure independent control valve the area of this orifice can also be changed by use of a mechanical actuator. This has the effect of allowing a maximum flow rate to be pre-set and modulating temperature control to be achieved in the same valve body.
Externally Adjustable Automatic Balancing Valve
A replaceable externally adjustable automatic balancing cartridge is used to maintain a constant water flow rate regardless of local fluctuations in differential pressure.
The automatic balancing cartridge includes an external scale that may be set to one of 50 individual positions by means of a radiator key and a micrometer type scale. The cartridge is supplied with a cap to prevent accidental re-setting of the cartridge. The externally adjustable balancing cartridge is available in 3 sizes 20mm, 40mm, and 50mm.
Rotary Pressure Independent Control Valve
A rotary pressure independent control valve is offered in sizes from ½” to 2” with flow rates up to 5 l/s. An internal pressure regulator keeps a constant differential pressure across a profiled ball which leads to a constant flow.
Maximum flow rate is set by limiting the position to which the ball can open. Temperature control is achieved by modulating the position of the ball whilst never opening beyond the maximum position.
The rotary pressure independent control valve is offered with a range of actuators including 3 point control, 10V control and a programmable multifunction actuator.
