Fluid handling – Self-proportioning or correlating systems – Self-proportioning flow systems
Patent
1989-06-19
1991-01-29
Hepperle, Stephen M.
Fluid handling
Self-proportioning or correlating systems
Self-proportioning flow systems
137503, 13762531, G05D 1103
Patent
active
049879162
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a liquid flow control device. In a preferred embodiment the invention is concerned with a device for metering controlled amounts of one liquid into another liquid flowing through a conduit at high pressures and flow rates.
The preferred device according to the invention finds particular use in controlling the injection of a surface-active agent into a fire water distribution system, to produce a foam when the water is released into a fire zone at atmospheric pressure. A typical class of agents is known as AFFF, aqueous film-forming foam, and is injected as a concentrate into the fire water to give a concentration of AFFF in the resultant solution of 1%, 3% or 6% according to operational requirements and the nature of the particular AFFF additive used.
On an offshore oil or gas platform the AFFF is injected into sea water for firefighting purposes, and the quantities of water required to be delivered by the firepumps can typically vary from 100 to 2250 m.sup.3 /hr. at pressure of around 15 bar. Flow rates and pressures will however vary in use according to the instantaneous demands for water being made on the system, and it is necessary to vary the injection rate in order to maintain the correct AFFF concentration in the water in spite of these fluctuations.
The currently used method of proportioning the AFFF to the water requires a main venturi to be installed in the conduit supplying fire water to the ring main on the platform, and a second venturi to be installed in the AFFF injection line. The AFFF is injected into the water at the throat of the main venturi. The AFFF is supplied to the second venturi at the same pressure as the water is supplied to the main venturi. The two venturis have flow coefficients in a fixed ratio, so that the ratio of AFFF introduced into the water at the throat of the main venturi is in the required proportion to the volume of water flowing. The disadvantages of this method include high pressure losses when working at high flow rates; low pressure losses at low flow rates, leading to inaccurate proportioning; and the readily available equipment having a maximum flow rate capability at the present time of only 1000 m.sup.3 /hr.
The present invention provides a flow control device with different characteristics, enabling some or all of these disadvantages to be mitigated.
In one aspect, the invention provides a flow control device for controlling liquid flow through a conduit, comprising a variable orifice in the liquid flow path in the conduit, a first branch line for liquid connected to the conduit upstream of liquid flow restriction means in the conduit, a second branch line for liquid connected to the conduit downstream of said liquid flow restriction means, and orifice control means operatively connected to the variable orifice and responsive to the liquid pressures in the first and second branch lines to vary the orifice to maintain a predetermined relation between the pressures in the said lines.
The orifice control means may comprise piston and cylinder means adapted to be driven by the liquid pressures in the first and second branch lines. The predetermined relation between the pressures in the said lines may for example be a pressure ratio, a pressure difference, or a combination of these, and will normally be determined by the design of the orifice control means.
The restriction may be a fixed restriction, such as a fixed orifice plate, downstream of the variable orifice, in which case the device can function as a flow regulator valve to maintain a constant liquid flow rate through the restriction. However, in the preferred application of the device, the restriction is the variable orifice itself, and the device then varies the flow coefficient of the orifice in order to maintain a predetermined relation between the pressures on either side of the variable orifice. Accordingly, in a second aspect, the invention provides a device for metering a second liquid into a liquid flowing through a conduit, comprising a flow control device as aforesai
REFERENCES:
patent: 1290 (1839-08-01), Kellogg
patent: 2496586 (1950-02-01), Kemp et al.
patent: 3047003 (1962-07-01), Gurney
patent: 3141471 (1964-07-01), Williamson
patent: 3642021 (1972-02-01), Muller et al.
patent: 3647002 (1972-03-01), Lindsay
patent: 4554943 (1985-11-01), Claney et al.
Hepperle Stephen M.
Hydro-Tec Limited
Usher Robert W. J.
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