MIXING AND PUMP SYSTEM

TECHNICAL FIELD

The present invention relates to the deicing of aircraft. More particularly, it relates to mixing and pumping systems for use by deicing vehicles for the mixing and pressurization of deicing fluid.

BACKGROUND ART

Within the air transport industry, it is important to have an effective deicing capacity during the winter months. For air safety, it is crucial that the wing surfaces of the airplane are fully cleaned, by which is meant that they have been cleaned of snow, ice, slush or frost. Even a. small ice creation affects the aerodynamics of the aircraft and its capacity to fly, especially at takeoff.

The harmful effects of so-called precipitation/ice creation can reduce the aerodynamic lift of the wing by up to 25%. In addition, snow, and ice affect the controllability and change the flight characteristics of the airplane; control surfaces, rudder surfaces and flaps freeze up, which can cause turbine damage, damage to retractable landing gear, ice particles can break loose and cause damage to the aircraft or objects on the ground, frozen sensors can wrong instrument readings.

For air transport companies, it is also important that the time on the ground is minimized in order to reduce the costs of having the plane standing unused. There is therefore a need for precise and rapid deicing.

SUMMARY

Vehicles which are provided with tanks for water and glycol, mixing and pumping systems and means for transporting the mixed fluid to a spray nozzle are known within the technical field. Compare, for example, the deicing vehicle SDI 213 from Safeaero (Trelleborg, Sweden). The present invention

relates to a mixing and pumping system which can accurately mix water and concentrated deicing fluid and provide high flows. A system for mixing and pumping deicing fluid comprises a water tank, a glycol tank, a water flow meter, a glycol flow meter, a computer-controlled water mixing valve, a computer-controlled glycol mixing valve and a powerful pump. The system is provided with piping for linking together the various tanks, the valves and the pump. The water tank is connected to a water flow meter, the water flow meter is connected to the water mixing valve, the water mixing valve is connected to one of two inlets to a T-coupling. The glycol tank is connected to the glycol flow meter, the glycol flow meter is connected to the glycol mixing valve, the glycol mixing valve is connected to a second input of the T-coupling. The outlet of the T-coupling is connected to the suction side of the pump. Further included are a water level transmitter and a glycol level transmitter disposed in the respective tank to measure the respective level. Also included in the system are a control system connected to said transmitters, meters, control valves and pump, which comprises means for accurately controlling and regulating flow and mixing ratio in an operator-controlled manner.

Thus the present invention relates to a system for mixing and pumping deicing fluid, comprising a water tank connected to a water flow meter, which water flow meter is further connected to a water mixing valve, which water mixing valve is further connected to one of two inputs of a T-coupling, a glycol tank is connected to a glycol flow meter, which glycol flow meter is connected to a glycol mixing valve, which glycol mixing valve is connected to a second input of the T-coupling, an outlet from the T-coupling is connected to a suction side of a pump, said system being provided with a constriction, which reduces the internal pipe diameter to an inlet to the glycol flow meter with a view to increasing the flow velocity of the glycol flow through said meter, and said system being further provided with a widening disposed after the meter in the direction of flow, so that the pipe diameter is widened to a diameter corresponding to the internal diameter of the pipe on a water side of said mixing system. The glycol flow meter is designed to measure more accurately at lower flows and, in addition, the connections are tailored to the smaller diameter of the connecting pipes. Said T-coupling is provided with two equal- sized inlets, which are arranged substantially symmetrically in relation to the outlet of said T-coupling.

Also included are a glycol level meter in the glycol tank and a level meter in the water tank, each meter producing a signal corresponding to the level in the respective tank. Further included in the system is a control unit, said control unit being provided with inputs for signals from the glycol flow meter and the water flow meter, as well as being provided with inputs for signals from the water level meter and the glycol level meter, and said control unit also being provided with inputs for manual inputting of the desired mixing ratio and desired flow quantity of mixed fluid, said control unit comprising means for allowing for the pressure additions arising from the level in the respective tank in order to be able to control the water mixing and glycol mixing valves so as to accurately achieve operator-input values for mixing ratio and flow.

The present invention further relates to a method usable in a system according to the above, comprising the following steps: Reading of a desired mixing ratio; Reading of the water level in the water tank; Reading of the level in the glycol tank; Reading of desired total fluid flow; - Based on desired mixing ratio, desired total fluid flow, glycol level and water level, creation of two control signals, one to the water mixing valve and one to the glycol mixing valve. In the creation of the control signal to the glycol mixing valve, the signal is designed such that the valve opens somewhat less when the level in the glycol tank is high, to compensate for gravitation- induced pressure additions. In the creation of the control signal to the water mixing valve, the signal is designed such that the valve opens somewhat less when the level in the water tank is high, to compensate for gravitation-induced pressure additions. Also included in said method is the step of making advance allowance for the extra pressure loss which occurs in flow through the aforesaid constriction, flow meter and widening compared with corresponding flow through the water flow meter and its connecting pipes.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments are described below with reference to the accompanying drawings, whereof: fig. 1 shows a schematic general view of a system according to one

embodiment of the invention.

DETAILED DESCRIPTION

Fig. 1 shows a mixing and pumping system 100 according to one embodiment of the present invention. A system for mixing and pumping deicing fluid comprises a water tank 102, a glycol tank 104, a water flow meter 114, a glycol flow meter 116, a controllable water mixing valve 120, a controllable glycol mixing valve 122, a T-coupling 130 and a pump 140. The system is provided with piping, which connects the various tanks, the valves and the pump to one another. The water tank 102 is connected to the water flow meter 114 via a non-return valve 110, the water flow meter 114 is connected to the water mixing valve 120, the water mixing valve 120 is connected to one of two inlets of the T-coupling 130. The glycol tank 104 is connected to the glycol flow meter 116 via a non-return valve 112, the glycol flow meter 116 is connected to the glycol mixing valve 122, the glycol mixing valve 122 is connected to a second of two inlets of the T-coupling 130. The outlet from the T-coupling is connected to the suction side of the pump 140.

The pipe connecting the glycol tank 104 to the glycol flow meter 116 is provided with a constricted section 115, which reduces the cross-sectional diameter of the pipe so that a higher flow velocity of the fluid is obtained through the glycol flow meter 116. After the glycol flow meter 116 in the direction of flow there is arranged a corresponding widening 117, which widens the diameter of this pipe to substantially the same size as the diameter of the pipe from the water tank 102. Preferably the diameters are the same. This has been shown to provide good preconditions for avoiding fluctuations in the mixing ratio and to give high accuracy in the measurement of low glycol flows, for example a glycol flow corresponding to a mixing ratio down to a 3% glycol contribution.

The T-coupling 130 is provided with two inputs of the same diameter and the actual T-coupling is preferably configured symmetrically and arranged so that, when the pump 140 starts up and creates an underpressure, fluid will be sucked through the T-coupling 130 and, depending on the setting of the mixing valves 120, 122, different amounts of fluid will be sucked from each tank 102, 104, depending on the setting of the mixing valves 120, 122. The water flow meter

114 and the glycol flow meter 116 are provided with means for converting measured flow into an electric signal representing the flow through the respective meter.

A control unit 150 is additionally provided, which receives said signals representing the flow and controls and regulates an output signal to the mixing valves 120, 122. The control unit 150 is provided with control and regulating means, which, based on input signals and/or set values from an operator control panel 160, adjust the mixing valves 120, 122 so that the desired flow is obtained and, moreover, the desired mixing ratio is obtained. From said control unit 150 there is also an output to said pump motor (not shown), which drives the pump 140 so that the power of the pump can be controlled. The pump 140 is preferably of the so-called screw type.

In addition, the water tank 102 is provided with a level sensor 106 and the glycol tank 104 is likewise provided with a level sensor 108, which produce a signal and which, via a connection between the sensor and the computer unit, convey to the computer unit this signal representing the level in the respective tank.

In the computer control unit, means are arranged which allow for the respective fluid level in the respective tank and adjust mixing valves and pump power so that optimal flow and accuracy in the mixing ratio are achieved.

A preferred embodiment of a method for controlling and regulating the mixing ratio between water and deicing fluid (ADF = anti-deicing fluid) comprises the steps:

Reading of desired mixing ratio; Reading of the water level in the water tank 102; - Reading of the level in the glycol tank 104; Reading of desired total fluid flow;

Based on desired mixing ratio, desired total fluid flow, glycol level and water level, creation of two control signals, one to the water mixing valve 120 and one to the glycol mixing valve 122.

The above steps are preferably carried out before the pump is started and

spraying is commenced. In the creation of the control signal to the glycol mixing valve, the signal is designed such that the valve opens somewhat less when the level in the glycol tank is high, to compensate for gravitation- induced pressure additions. The same applies in the creation of the control signal to the water mixing valve. Also preferably included is the step of making advance allowance for the additional pressure loss which occurs in flow through the constriction 115, the flow meter 116 and the widening 117 compared with corresponding flow through the water flow meter 114.

When the pump is started, the method also includes the steps:

Reading of the glycol flow;

Reading of the water flow;

Calculation of the current mixing ratio;

Comparison of the current mixing ratio with the desired mixing ratio; - Adjustment of the control signals of the valves 120, 122 if the current mixing ratio differs more than marginally from the desired mixing ratio.

In such an adjustment, an allowance is made for the dynamically reducing fluid quantity in the respective tank.