How to verify the dosing rate of a water driven pump proportioner

During the market transition from AFFF to SFFF (fluor free concentrates) it is important to know the viscosity of the SFFF concentrate, to choose the right type of proportioner

As regulatory authorities now are pushing for soonest possible transition from PFAS-containing concentrates to SFFF concentrates, many proportioning systems are re-evaluated to ensure compatibility. Different concentrate manufacturers offer a variety of foams which comes in a wide range of viscosities, including very high viscous fluids. To be able to select a compatible proportioner one needs to know the properties of the concentrate.

Proportioners with Gear Pump 


Water motor driven pump proportioner equipped with a Gear pump are suited for high and very-high viscosity concentrates, when the proportioner is operating in the higher range of a systems maximum flow rate, such as deluge and large fire monitor systems. Firemiks has with excellent result tested Gear pumps models with a Fluorine-free foam with 8,000 cP (Brookfield Viscometer Spindle #4 at 30 rpm). The reason Gear pumps works well with these very-high viscous concentrates is that they are equipped with robust counter rotating gears which seals better with high viscosity fluids and creates a continuous flow that does not agitate the concentrate. FIREMIKS model equipped with a Multi V-rib belt drive increases pump rpm making it possible to use Gear pumps also when using medium viscosity concentrates. 



Proportioners with Piston Pump


Water motor driven pump proportioners equipped with Piston (plunger) pumps are on the other hand suited for use in systems using low and medium viscosity concentrates, and the pump works from low start-up flows in relation to the systems maximum flow rate, for example sprinkler system applications, due to the flat pump curve profile that piston pumps have. Important to know is that Piston pumps have a limit upwards to high viscosity concentrates, normally around 4,000-4,500 cP (Brookfield Viscometer Spindle #4 at 30 rpm) due to the Piston pump reciprocating principle; for each revolution, the plunger sucks concentrate and then presses it out and the concentrate goes from zero to full speed twice per revolution. If the static viscosity is too high with non-Newtonian concentrates, the concentrate will not flow smoothly and therefor the correct dosing rate might not be achieved. 

FIREMIKS is uniquely positioned to offer proportioners with both types of pumps, Gear and Piston (a selected line of 3% piston pump models is FM-approved). This combined with our sturdy multi-vane motor that offers optimal reliability based on 40 years field experience. Among several important factors, besides flows and pressures, we always gather info from the customer regarding the concentrate type and viscosity before we propose which type of pump that will match the customers need.  Important for all systems is that one should ensure that diameter on the foam supply piping is large enough for the concentrate delivery and to avoid longer concentrate lines. Recommendations are specified in our Data sheet for each model.  


Functional testing of FIREMIKS water driven pump proportioner with Dosing return valve 


To enable easy and quick functional testing of the proportioner Firemiks offer the option DRV (Dosing return valve). With this feature one can test the unit without consuming the concentrate, allowing for an easy regular inspection of the unit. With an added flow meter and pressure valve on the return line to the concentrate tank, to simulate the water back pressure, one gets a concentrate volume/min to be calculated together with water flow measurements to achieve the actual dosing rate. This gives substantial saving of costs during many years. Apart from no consumption of concentrate there is no cost for cleaning up and destruction of dispersed foam after the test, an important environmental benefit if choosing this option. 

One example: an 8000 lpm unit with 3% dosing rate. 4 tests/year at max speed for one minute. 8,000 lpm x 3% = 240 litre of foam concentrate x 4 times = 960 litre at for example a cost of 3 euro/lit = 2,880 Euro.- in saved cost/year apart from savings on clean-up costs of dispersed foam. 

How to correctly verify the dosing rate by measuring water flow and dosing pump flow 

To verify the dosing rate, one needs to verify the correct volumetric function of both the water motor and the dosing pump. The accurate way to obtain this is to verify the water flow through the water motor with a calibrated independent flow meter, and the concentrate flow pumped by the dosing pump with a calibrated independent flow meter. Thereafter calculate the figures obtained to the formula in accordance with EN 13565-1, NFPA 11, FM 5130: 

(Concentrate flow) / (Water flow + Concentrate flow ) x 100 = Dosing rate %


To use an independent water flow meter is also the only correct method to validate the performance of the water motor, i.e. that it is keeping its designed volumetric function. 

Revolution counter with flow rate display 

A revolution counter with flow rate display can be used as a convenient way of estimating the water flow through the water motor. This can help e.g. to get an indication of overflow in a system.  As described by FM Approval guide:  ...may be used to provide a general estimate of the extinguish water flow…” 

Revolution counting with handheld Tachometer 

An alternative way to measure the rpm is to use a digital hand-held tachometer (contact or non-contact) to verify rpm, and then compare the value with the max flow rpm as shown on our Data sheets. This is recommended to ensure that a unit is not over-speeding, i.e working within the upper flow limit specified in Data sheets. 

The limits of revolution counter method 

The revolution counter method assumes the correct functioning of the water motor to give an estimate of water flow. This means that it cannot be used to correctly verify the dosing rate, as the dosing rate is directly dependent on the performance of the water motor, which is not verified by this rpm method.  
Likewise, it would be possible to estimate the concentrate flow of the concentrate pump by using the rpm method, and similarly this would not be a valid method to verify the dosing rate. 

The revolution counter method is not an approved method to verify dosing rate as described by EN 13565-1, NFPA 11, FM 5130.  

Alternative method to measure pumped concentrate 

An alternative method to measure the pumped concentrate that do not require a flow meter, is to pass it into a separate container and weight the amount during a defined time (Nordtest method NT Fire 042). 

You are always welcome to contact us for guidance and recommendations on practical solutions how to calculate dosing rate for a specific project.