WRPs, Wide range proportioners
This type of proportioners provides a very wide flow range by varying the area of the foam orifice and of the water inlet, in other words, a sufficient pressure drop at low flows can be maintained. With the aid of a spring and a piston, this is achieved when the piston moves due to a higher flow, the foam liquid orifice is then exposed with the same area proportions as the piston in the water flow.
An AAAF liquid, for example 3%, have a foam area of 3% of the water area. With a non-Newtonian fluid, consideration must be given to the viscosity versus pressure drop and area and shape of the area. Area compensation can be significant on low flows with lower pressure drop, but contrary to the higher flows.
Viscosity labeling of non-Newtonian liquids as prescribed by the standard is very misleading. Non-Newtonian gives a warning that the hydraulic laws do not apply. In other words, this marking must be ignored and foam tests must be conducted and new foam orifices have to be made.
We have had the opportunity to try for UL and FM listings of these products for Johnson Control and Solberg
The sizes DN 150, 200 and 250 are available as standard.