Pool Filter Pressure Gauge

This invention relates to liquid pressure gauges, and more particularly, is concerned with a pressure gauge for use in combination with swimming pool filters.

Diatomaceous earth type pool filters require that the earth material be replaced when the filter becomes dirty through continuous use. To determine when the filter material should be replaced, it has been the practice to provide an indication of the inlet pressure to the filter. Dirt removed from the water gradually clogs the pores of the diatomaceous earth thereby increasing the back pressure on the pump.

It has been the practice in the past to provide a conventional Bourdon type pressure gauge which is connected to the top of the filter housing on the inlet side of the filter. Associated with the coupling gauge is a stop cock or valve for bleeding off air which may become trapped in the top of the filter housing. The combination of the valve, pressure gauge, and coupling to the top of the filter, which conventionally are made of brass, add a substantial cost to the pool filter installation.

The present invention is directed to an improved pressure gauge which may be constructed entirely of plastic materials without moving parts. The gauge incorporates means for bleeding air from the filter so as to eliminate the need for a separate bleeder valve.

This is accomplished, in brief, by providing a housing of transparent plastic material forming a chamber therein with means for fluid coupling the chamber to the top of the pool filter. The housing includes a removable cap for opening and closing the chamber to the atmosphere. A tubular member attached to the inside of the cap extends vertically downward inside the housing, the lower end of the tubular member being open to the interior of the chamber and the top of the tubing being sealed. A cup-shaped member is positioned inside the chamber which opens adjacent the top of the chamber above the level at which liquid enters the chamber. The lower end of the tubular member extends downwardly inside the cup-shaped member so that the level of the liquid entering the chamber must rise above the top of the cup-shaped member to fill the cup-shaped member with liquid and trap air in the tubular member. The level to which liquid rises in the tubular member provides an indication of the water pressure in the filter.

For a more complete understanding of the invention reference should be made to the accompanying drawing, wherein:

FIG. 1 is an elevational view of the invention installed in a pool filter;

FIG. 2 is a sectional view of the pressure gauge; and

FIG. 3 is a top view of the gauge with the cap removed.

Referred to the drawing in detail, the numeral 10 indicates the top of a conventional pool filter. The interior of the filter housing is filled with water from the discharge side of the pool circulating pump. This may cause air to be trapped in the top of the filter, particularly after the filter housing has been open to clean or replace the filter material. It has been the practice in the past to provide some type of stop cock in the filter top to bleed off this air to insure that the filter is completely filled with circulating pool water. Also it has been the practice in the past that a T-connection is provided in connection with the stop cock to which a conventional Bourdon tube pressure gauge is connected to indicate the fluid pressure in the top of the filter unit. For this purpose, the top of the filter housing is provided with a lug 12 having a threaded opening 14 for connecting to a bleeder valve and standard pressure gauge.

The pressure gauge according to the present invention, indicated generally at 16, includes an outer housing 18 of general cylindrical shape terminating at its lower end in a threaded nipple 20 for attaching the gauge to the filter. A fluid passage 22 through the center of the nipple 20 provides fluid communication from the interior of the filter into a chamber 24 in the inside of the housing 18.

The upper end of the housing 18 is open and is adapted to receive a threaded cap 26 which screws down over the open end of the housing 18. A suitable gasket, such as an O-ring 28 is inserted between the inside of the cap 26 and the top of the housing 18 to provide a fluid-tight seal when the cap 26 is tightened down on the housing. Supported on the inside of the cap 26 and extending down into the chamber 18 is a tubular member 30. The tubular member 30 includes a lower section 32, an intermediate section 34, and an upper section 36. The lower section 32 if of slightly larger diameter than the intermediate section 34, a slight step 38 being formed at the junction between the lower and intermediate sections of the tubular member 30. The top section 36 is enlarged in diameter to form an enlarged volume at the top of the tubular member 30. The upper portion 36 is integral with the top of the cap 26 so that the tubular member 30 and the cap 26 form an integral structure. The lower end of the tubular member 30 is provided with a bottom plate 40. One or more small openings 41 are formed adjacent the bottom plate 40 to provide fluid communication between the interior of the tubular member 30 and the chamber 24.

Also inserted in the chamber 24 is a cup-shaped member 42 which is separate from the housing 18 and the cap 26. With the cap 26 removed, the cup-shaped member 42 may be inserted in the chamber 24. The wall of the cup-shaped member is held in concentric relation to the housing 18 by a plurality of external ribs 44. The bottom of the cup-shaped member is spaced from the bottom of the housing 18 by integrally moulded lugs 46. The top of the cup-shaped member 42 is roughly even with the top of the housing 18 and is spaced from the inside of the cap 26 by roughly the thickness of the O-ring gasket 28.

Thus it will be seen that with the gauge 16 mounted in position on the top of the filter water may enter the passage 22 from the filter, pass upwardly in the spaces between the outside of the cup-shaped member 42 and the interior of the housing 18 over the top edge of the cup-shaped member 42 so as to fill the cup-shaped member. The cap 26 must be loosened to permit air to escape from the top of the chamber 24. It is displaced by the water being forced upwardly into the chamber from the filter. As the water level rises inside the cup-shaped member 42, air is trapped inside the tubular member 30. As the pressure of the water increases, the trapped air in the tubular member 30 is compressed and the level of the water in the tubular member rises by an amount dependent on the pressure of the water in the filter. By making the parts of the gauge of a transparent plastic material, the level of the water inside the tubular member 30 can be observed. To make the level more visible, a float in the form of a small colored bead 46 is placed inside the tubular member 30. The bead floats on the surface of the water as it rises in the tubular member, thus providing a clear indication of the level of the water. A suitable scale may be inscribed on the outside of the housing, as shown in FIG. 1, for calibrating the level of the bead in units of pounds of pressure.

Normally the step 38 is positioned to correspond to the normal operating pressure of the pool filter system. Small changes in pressure within the normal range, because of the larger cross-sectional area of the lower end of the tubular member 30, do not produce significant change in the level of the water within the tubular member. However, as the filter becomes dirty and the pressure level builds up, once the level extends into the reduced diameter intermediate section 34, the amount of level change with a given incremental pressure change is increased, providing an expanded scale in this region. This offsets the normal exponential relationship between pressure and change in volume which would otherwise tend to compress the scale as the pressure increased. The enlarged volume at the upper end 36 of the tubular member allows adjustment of the scale range on the side of the housing to the desired operating range of the system.

From the above description it will be seen that a very simple gauge is provided which can be readily moulded from plastic materials and which requires no moving parts for its operation. The cap of the gauge provides a means of bleeding air from the filter system. The cup-shaped member 42 retains water surrounding the tubular member 30 even though some air may accumulate in the filter and enter the chamber 24 of the gauge. Thus the gauge continues to function even though the filter system may have some air leakage in the system.