GB2152394A

GB2152394A - Balanced-pressure liquid additive induction system

Info

Publication number: GB2152394A
Application number: GB08431627A
Authority: GB
Inventors: Robert Alec Lewis
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-01-14
Filing date: 1984-12-14
Publication date: 1985-08-07
Also published as: GB8401015D0; GB8431627D0

Abstract

An additive is added to a primary liquid flowing in a pipeline (6) to a pump (3) through pipe work (10, 14) and induction device (13). A pressure-balancing valve (11) is incorporated in the pipework (10, 14) so that the additive inlet pressure is reduced to equal that of the primary liquid at or near the bottom of the tank (1). The pressure balancing valve 11 incorporates a diaphragm (17), which directly or indirectly senses the pressure at the bottom of the primary tank 1, and is connected to a valve (18) which controls the pressure of the additive feed. Alternatively it may incorporate a sliding element, or be mechanically or electrically actuated in response to means which mechanically or electrically sense the pressure in the tank (1). The system is used on fire-fighting vehicles for mixing additives with primary extinguishing media such as water. The pressure balancing valve (11) allows an approximately constant mixing ratio to be achieved over a wide range of flows regardless of the levels of additive or primary extinguishing agents in their tanks. <IMAGE>

Description

SPECIFICATION Balanced-pressure liquid additive induction system This invention relates to a balanced-pressure liquid additive induction system.

Fire fighting vehicles generally incorporate a tank which contains a primary fire extinguishing media.

This primary fire extinguishing media, which is hereafter referred to as the primary agent, is normally water. Under certain circumstances it is desirable to mix an additive or additives with the primary agent to improve its extinguishing properties or to reduce friction losses in fire hose.

The primary agent is normally fed from its tank through fixed pipework to a pump which is mounted on the vehicle and is generally driven by the vehicle's own prime mover. A valve is normally incorporated in this fixed pipework. If this valve is open but there is no delivery from the pump, then the pressure of the primary agent in this pipework is equal to the static head of primary agent in its tank. When the pump is delivering this pressure is reduced and there is flow in the pipework. This reduction in pressure and the velocity of the flow can be used to induce an additive into the primary agent.

There are various known methods of inducing the additive, using venturi and the like, which will give an approximately constant mixing ratio of additive to primary agent over a wide range of flow rates provided that the pressure of the primary agent and the additive where they enter the mixing area are balanced. If the pressures are not balanced, then the mixing ratio will change as the levels of the primary agent in its tank or the additive in its tank change. A typical balanced pressure induction system comprises a flexible bladder containing the additive which is mounted inside near the base of the primary agent tank so that it senses the head of primary agent in its tank. This flexible bladder is connected by pipework to a metering and induction system which are remote from the primary agent tank and generally incorporated in the pipework from the primary agent tank to the pump.

According to the present invention there is provided a balanced pressure additive induction system comprising a tank containing a primary agent, another tank containing an additive, pipework from the primary agent tank to a pump, means for inducing additive into the primary agent between its tank and the pump and pipework from the additive tank to this induction device which pipework incorporates a pressure balancing valve. The pressure balancing valve senses the pressure of the primary agent at or near the bottom of the primary agent tank and controls the pressure of the additive feed to the induction device so that it balances the pressure of the primary agent at or near the bottom of its tank.

Such an arrangement allows an additive to be mixed with a primary agent at an approximately constant mixing ratio over a wide range of flow rates and it automatically compensates for changes in the levels of the primary agent or the additive in their tanks.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which Figure I shows the diagrammatic layout of the complete additive induction system; Figure 2 shows the pressure balancing valve in cross-section; and Figure 3 shows the additive flow metering and induction assembly in cross-section.

Referring to the diagrammatic layout, Fig. 1. the system comprises a primary agent tank 1, an additive tank 2, and pipework connecting these to a pump 3.

The primary agent tank 1 incorporates a sump pot 4 which has a horizontal outlet connection 5.

The primary agent flows from outlet connection 5 through pipework 6 to the suction inlet of pump 3.

This pipework incorporates valve 7.

The primary agent tank 1 also incorporates a pressure sensing connection 8 at or near the bottom of the tank. The pressure may be sensed using the primary agent to provide the pressure signal or it may be sensed by using an intermediate fluid such as air to provide the pressure signal, in which case a bladder 9 will be connected to pressure sensing connection 8.

The additive tank 2 is located above the top of the primary agent tank 1 and the additive flows from it through additive tank outlet pipe 10 to pressure balancing valve 11. The pressure balancing valve 11 is located so that it is approximately at the same horizontal level as the primary agent pressure sensing connection 8. The pressure balancing valve 11 is connected to the pressure sensing connection 8 by pressure sensing pipe 12.

The additive flows at a controlled pressure from the pressure balancing valve 11 to an additive flow metering and induction device 13 through additive feed pipe 14.

The additive flow metering and induction device 13 controls the ratio of mixing of the additive with the primary agent.

The construction of the pressure balancing valve 11 is shown in cross-section in Figure 2. The pressure balancing valve 11 comprises a pressure sensing housing 15, a pressure controlling housing 16, and a flexible sealing diaphragm 17, which is connected to valve 18, which controls the flow of additive through orifice 19. The pressure sensing housing 15 has a connection 20 onto which pressure sensing pipe 12 is attached. The pressure controlling housing 16 incorporates an additive inlet pipe 21 which also acts as a guide for valve 18.

The pressure controlling housing 16 also incorporates an additive outlet connection 22 which is connected to additive feed pipe 14. The pressure balancing valve 11 may incorporate spring 23 in the pressure sensing housing 15 and/or spring 24 in the pressure controlling housing 16 in order to adjust the opening characteristics of valve 18. Orifice 19 is thus controlled by the pressures acting on diaphragm 17 so that it controls the additive pressure downstream of orifice 19 in response to the pressure of the primary agent.

Alternatively the pressure balancing valve 11 may incorporate a sealed sliding element in place of the diaphragm 17.

Alternatively the pressure balancing valve may incorporate a valve 18 which is electrically actuated by a signal from a pressure sensing device at or near the bottom of the primary agent tank 1.

Alternatively the pressure balancing valve may incorporate a valve 18 which is mechanically actuated by a linkage from a pressure sensing device at or near the bottom of the primary agent tank 1.

The additive flow metering and induction device 13 may vary in type and design. A typical flow metering and induction device is shown in cross-section in Figure 3. The assembly comprises a housing 25 which is fitted to the pipework 6. This housing 25 is constructed so that its inner face 26 is tangential to the inside diameter of the pipework 6. The connection of the housing 25 to the pipework 6 should be made in a region of the pipework 6 where the primary agent flow is not excessively turbulent. A metering orifice plate 27 is trapped between the union 28 of the additive feed pipe 14 and the housing 25 by the union nut 29.

The solution of additive in water flows to the pump 3, in which it is pressurized for delivery through one or more hoses which are equipped with nozzles which project the additive solution onto the fire or hazardous matterial. The additive may be a foaming agent, in which case the nozzles will be of the aerating type.

Claims

1. A balanced pressure liquid additive induction system comprising a tank for containing a primary agent, another tank for containing an additive, pipework from the primary agent tank to pump, means for inducing additive into the primary agent between its tank and the pump, the pipework from the additive tank to this induction device which pipework incorporates a pressure balancing valve which is responsive to the pressure of the primary agent at or near the bottom of the primary agent tank and controls the pressure of the additive feed to the induction device so that it balances the pres sure of the primary agent at or near the bottom of its tank.

2. A balanced pressure liquid additive induction system as in claim 1 wherein the pressure balanc ing valve incorporates a diaphragm which directly or indirectly senses the pressure of the primary agent at or near the bottom of the primary agent tank and controls an additive feed valve.

3. A balanced pressure liquid additive induction system as in claim 1 wherein the pressure balanc ing valve incorporates a sealed sliding element which directly or indirectly senses the pressure of the primary agent at or near the bottom of the pri mary agent tank and controls an additive feed valve.

4. A balanced pressure liquid additive induction system as in claim 1 wherein the pressure baianc ing valve is electrically actuated by a sensing means which signals the pressure of the primary agent at or near the bottom of the primary agent tank and controls an additive feed valve.

5. A balanced pressure liquid additive induction system as in claim 1 wherein the pressure balancing valve is mechanically actuated by a sensing means which senses and mechanically signals the pressure of the primary agent at or near the bottom of the primary agent tank and controls an additive feed valve.

6. A balanced pressure liquid additive induction system substantially as described herein with reference to Figures 1-3 of the accompanying drawings.