SYSTEM FOR CONTROLLING THE STROKE OF AN AIR-OPERATED DOUBLE DIAPHRAGM PUMP

Abstract

A system for controlling the stroke of an air-operated double diaphragm pump includes a first control valve and a second control valve disposed in parallel within a drive air outlet conduit. The first flow control valve has a first air flow capacity and the second flow control valve has a second air flow capacity which is less than about 50% of the first air flow capacity.

Description

BACKGROUND OF THE INVENTION

Double diaphragm pumps are commonly used to meter out specific quantities of a fluid from a first location to a second location. For example, double diaphragm pumps are frequently used to meter out specific quantities of concrete coloring agent from coloring agent holding tanks to concrete disposed in a delivery truck. (See, for example, FIG. 2.) In this application, and in many other applications, it is important to meter out the desired precise amount of material—and not less and not more.

An inherent problem, however, with double diaphragm pumps is their propensity for delivering a surge of material at the end of a pumping cycle. Typically, as a pumping cycle nears completion, the drive air inlet valve is reduced and/or the pressure of the inlet side drive air is reduced so that the pump slows down. However, even at such reduced pumping rates, the double diaphragm pump surges significantly as the pumping cycle is completed. For example, the surge of a typical one and one half inch air-operated double diaphragm pump, wherein the drive air is throttled as the cycle is completed, surges approximately 0.2 gallons as the cycle comes to an end.

This cycle ending surge is a significant problem for those attempting to use air-operated double diaphragm pumps to meter out a precise quantity of material. Accordingly, there is a need for a system for controlling the stroke of an air-operated double diaphragm pump which significantly reduces this problem.

SUMMARY

The invention satisfies this need. The invention is a system for controlling the stroke of an air-operated double diaphragm pump, the pump having a drive air inlet and a drive air exhaust outlet, the system comprising (a) an air outlet conduit connected in fluid tight communication with the drive air exhaust outlet, (b) a first flow control valve operatively connected in fluid tight communication with the air outlet conduit, the first flow control valve having a first air flow capacity, and (c) a second flow control valve operatively connected in fluid tight communication with the air outlet conduit, the second flow control valve being connected in parallel with the first flow control valve and having a second air flow capacity which is less than about 80% of the first air flow capacity.

DRAWINGS

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims and accompanying drawings where:

FIG. 1 is a diagrammatic representation of a double diaphragm pump system having features of the invention; and

FIG. 2 is a diagrammatic representation of a system for providing liquid coloring agents to concrete mixtures within concrete delivery vehicles, having features of the invention.

DETAILED DESCRIPTION

The following discussion describes in detail one embodiment of the invention and several variations of that embodiment. This discussion should not be construed, however, as limiting the invention to those particular embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well.

The invention is a system 10 for controlling the stroke of an air-operated double diaphragm pump 12. One embodiment of the invention is illustrated in FIG. 1.

The pump 12 has a suction side 14 and a discharge side 16. Product to be pumped is conveyed to the suction side 14 via a suction side conduit 18. The product is conveyed away from the discharge side 16 via a discharge side conduit 20.

The pump 12 is driven by compressed drive air. The pump 12 thus comprises a drive air inlet 22 and a drive air exhaust outlet 24. Compressed drive air is provided to the drive air inlet 22 via a drive air inlet conduit 26. Drive air exhaust is transmitted away from the drive air exhaust outlet 24 via an air outlet conduit 28.

A first flow control valve 30 is operatively connected in fluid tight communication with the air outlet conduit 28. Typically, the first control valve 30 is a solenoid valve, but other valves can also be employed. Typically, the first flow control valve 30 is sized to be of similar diameter to that of the exhaust port of the pump 12.

The first flow control valve 30 is sized and dimensioned to handle a large flow capacity, so as to withdraw exhaust air from the drive air exhaust outlet 24 rapidly. The first control valve, therefore, has a large first air flow capacity.

In the embodiment illustrated in FIG. 1, an optional muffler 32 is disposed downstream of the first flow control valve 30 so that noise from exhaust air being discharged to the atmosphere downstream of the first flow control valve 30 is reduced.

A second flow control valve 34 is operatively connected in fluid tight communication with the air outlet conduit 28 and is disposed in parallel with the first flow control valve 30. The second flow control valve 34 has a second air flow capacity which is markedly less than that of the first air flow capacity. Typically, the second air flow capacity is less than about 50% of the first air flow capacity, typically between about 10% and about 20% of the first air flow capacity, and can be adjusted by the user.

The system 10 of the invention can be used to provide a method for pumping a precise quantity of fluid. In the method, the first flow control valve 30 is initially open. Product is then pumped via the air-operated double diaphragm pump 12 while the first flow control valve 30 rapidly removes exhaust air from the pump 12, so that the pump 12 operates at a high initial flow rate. In the method, greater than about 95% of the precise quantity of product is thus pumped at such high rate of flow.

Once the greater than about 95% of the precise quantity of fluid has been pumped, the first flow control valve 30 is closed. Thereafter, the remainder of the precise quantity of fluid is pumped via the air-operated double diaphragm pump 12 at a reduced flow rate—because of the reduced air flow capacity of the second flow control valve 34.

Once the entirety of the precise quantity of fluid has been pumped, the pump 12 is shut down. By the above-described method, it has been found that typical end-of-cycle surging caused by the air-operated double diaphragm pump 12 are markedly reduced. For example, it has been found in a typical one and one half inch double diaphragm pump 12 that the end-of-cycle surge is reduced to only about 10% of the surge typically encountered in prior art air-operated double diaphragm pump 12 systems.

Those of skill in the art will recognize that the above-described system and method can be used in a wide variety of applications. FIG. 2 illustrates one such application wherein the system 10 and method are conveniently adapted for providing liquid coloring agent to concrete delivery vehicles 36 parked in a loading zone.

As shown in FIG. 2, differing liquid coloring agents are initially respectively disposed in a plurality of bulk tanks 38. An air-operated double diaphragm pump 12 is connected in fluid tight communication to each bulk tank 38. Each air-operated double diaphragm pump 12 is equipped with the system 10 of the invention. Liquid coloring agent can, therefore, be precisely removed from a bulk tank 38 and delivered to a delivery vehicle 36 parked in the loading zone. Prior problems with measuring the precise quantity of liquid coloring agent for transfer to a delivery vehicle 36, due to excessive end-of-cycle surging, has been markedly reduced by the system 10 and method of the invention, thereby markedly increasing the reproducibility of the concrete color transported by each delivery vehicle 36.

Having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims.

Claims

1. A system for controlling the stroke of an air-operated double diaphragm pump, the pump having a drive air inlet and a drive air exhaust outlet, the system comprising:

(a) an air outlet conduit connected in fluid tight communication with the drive air exhaust outlet;

(b) a first flow control valve operatively connected in fluid tight communication with the air outlet conduit, the first flow control valve having a first air flow capacity; and

(c) a second flow control valve operatively connected in fluid tight communication with the air outlet conduit, the second flow control valve being connected in parallel with the first flow control valve and having a second air flow capacity which is less than about 50% of the first air flow capacity.

2. The system of claim 1 wherein the second flow control valve has a second air flow capacity which is between about 10% and about 20% of the first air flow capacity.

3. A method for pumping a precise quantity of fluid using an air-operated double diaphragm pump, the pump having an air inlet and a drive air exhaust outlet, the method comprising the steps of:

(a) providing the system for controlling the stroke of the air-operated double diaphragm pump of claim 1;

(b) opening the first flow control valve;

(c) pumping greater than about 95% of the precise quantity of fluid at a high rate of flow;

(d) closing the first flow control valve; and

(e) pumping the remainder of the precise quantity of fluid at a reduced rate of flow.

4. The system of claim 3 wherein the second flow control valve has a second air flow capacity which is between about 10% and about 20% of the first air flow capacity.

5. A system for providing liquid coloring agent to concrete delivery vehicles parked in a loading zone, the system comprising:

(a) a plurality of bulk tanks;

(b) an air operated double diaphragm pump connected in fluid tight communication to each bulk tank, each double diaphragm pump having a drive air exhaust outlet;

(c) an air outlet conduit connected in fluid tight communication with each drive air exhaust outlet;

(d) a fill line connecting each double diaphragm pump to the loading zone; and

(e) a system for controlling the stroke of each air-operated double diaphragm pump comprising (i) an air outlet conduit connected in fluid tight communication with the drive air exhaust outlet, (ii) a first flow control valve operatively connected in fluid tight communication with the air outlet conduit, the first flow control valve having a first air flow capacity, and (iii) a second flow control valve operatively connected in fluid tight communication with the air outlet conduit, the second flow control valve being connected in parallel with the first flow control valve and having a second air flow capacity which is less than about 50% of the first air flow capacity.

6. The system of claim 5 wherein the second flow control valve has a second air flow capacity which is between about 10% and about 20% of the first air flow capacity.