To set a sample or a purge flow, whether in a laboratory or for a pilot plant, it is simplest to use a manual control on the flow of liquid or gas from the supply or the pump
Within the range of Platon variable area flowmeters, the typical meters used as flow indicators, the NGXV models are supplied with an integral flow control valve for manual adjustment.
Typically a glass tube flowmeter will operate over a 10:1 flow range, and the fine control valve supplied with the frame will easily control all such flows.
Platon also manufacture the Platon FCV - a stand-alone multi-turn Fine Control Valve - which allows precision adjustment of fluid flows, suitable for use on gas flows up to 100litres/minute (liquids to 3.5l/min), in piping systems typically using standard 1/4BSP (G1/4) connections: these are common in laboratories and pilot plants or sample/purge flow systems.
The Platon FCV gives precision control over a wide flow range, typically 100:1.
In a flow system, the pump or the storage system pressure will vary, either as the demand from other users changes, or as the fluid in the tank is discharged.
This can lead to a variation of the flow delivered, through the simple manual FCV control valve.
Similarly in sampling systems, the sampled flow conditions might change, or the sample analysis or collection and storage system might provide a variable back pressure, resulting in an undesirable change in the sample flow rate.
Many such site condition changes can be overcome, and a steady flow maintained, by using a simple mechanical flow controller, known as a Platon Flostat.
The MN Flostat is a mechanical device, which uses the flow pressure across an orifice to act against a spring loaded diaphragm, within the Flostat, to control the flow to a fixed value, preset using an integral multi-turn needle valve: typically the MN Flostat is used in series with the Platon NGX flowmeter to show the operator the actual flow rate being delivered.
A differential pressure is required across the Flostat for it to function: the largest MN Flostats suitable for 1/4BSP applications can control gas flows from 8-100l/min and liquids from 0.25-3.5l/min, whereas the smallest range units control 0.005-5l/min gas and 0.002-0.2l/min water.
Once set, the flow rate will be maintained constant, subject to the differential pressure required being maintained across the Flostat: the constant flow rate will be visible on the NGX flowmeter.
Flostats are ideal for blending or dosing applications to maintain the required delivery of valuable gases or liquids, despite variations in the process line pressure.
Similarly, Flostats are ideal for use on gas sampling, blending, purging or inert gas tank blanketing systems to maintain flow rate independent of the back pressure in the delivery vessel.
Bubbler type liquid level measurement systems benefit from improved accuracy and lower gas usage when fitted with a Flostat.
Other Flostats have been used to control the delivery of aviation fuel into aircraft tanks to a certain safe maximum rate, whatever power the generator driven pump might have been providing.
Because the Flostat is a mechanical controller, it requires no power, and there is no problem with using the device in a hazardous area or for the control of flammable liquids.
Special versions have been produced for use with larger flows, in bigger diameter pipes, and for higher absolute pressure applications.
