GB2216823A - Compressed gas drying system - Google Patents

Abstract

In a compressed air system a compressor (1) charges reservoirs (not shown) via an air dryer (6) which requires regeneration from time to time by purging with a metered flow of dry air, a cut-off valve (5) is included in the input line to the air dryer which is thereby closed during purging and the compressor is permitted to continue running on load to charge a further storage vessel (3). The system also comprises a condenser (2). <IMAGE>

Description

Compressed Gas Systems This invention relates to compressed gas system and relates especially to compressed gas systems wherein a gas compressor supplies gas at a pressure higher than atmospheric pressure via a gas dryer to utilisation meat or a storage reservoir.

Compressed gas systems are well known especially for compressed air operable vehicle braking and in such systems over the past decade it has increasingly become practice to include an air dryer in the charging line between an engine-driven piston and cylinder compressor and valve means to one or more storage reservoirs.

An air dryer usually comprises a housing containing a suitable granular desiccant material through which the gas is passed. The desiccant is regenerated from time to time by allowing metered flow of a relatively small volume of dry air back through it when the compressor Is is off-load or cut out. Such a process/commonly known as purging. This can lead to the air dryer not operating properly in cases where the compressor has capacity which is little if no more than'the air usage requirements because in that case the compressor will only infrequently cut out or go off-load. Purging'then occurs at best only infrequently and the benefits of the air dryer may be lost.One way of reducing this problem is to include an air dryer which has two sections that operate alternatively and some means for causing one section to be purged whilst the compressed air flow is switched through the other section. However, such an air dryer tends to be expensive especially bearing in mind that it may only be required for a proportion of systems, namely where the capacity of the compressor is close to the volume requirement of the system.

An object of the present invention is to provide an improved compressed gas system wherein the above shortcoming is reduced.

According to the present invention there is provided a compressed gas system including a gas compressor coniiected to a reservoir or utilisation means via a cut-off valve, and a gas drying means responsive to a control signal to from time to time close the cut-off valve and initiate regeneration of the gas drying means a storage vessel being connected to a point between the compressor and the cutoff valve and into which vessel compressed gas can thereby flow from the compressor whilst the cut-off valve is closed.

In order that the present invention may be more clearly understood and readily carried into effect the same will be further described by way of examples with reference to the accompanying drawings of which Figs. 1 to 3 illustrate various embodiments of systems in accordance with the invention.

Referring to Fig. 1 of the drawings, this shows a compressed air reservoir-charging system for the compressed air systems of a heavy vehicle. The engine of the vehicle is fitted with an air compressor denoted by reference 1, connected via a condenser 2 to a reservoir 3. The connection between the reservoir 3 and the condenser: is made via a so-called single circuit protection valve 4 which is capable of persiting "feed-back" of compressed air down to a pre-aetermined level. The single circuit protection valve 4 is, therefore, a valve of known type which allows forward charging from the condenser into the reservoir 3 and in the event of the supply pressure collapsing for any reason, the pressure in 3 is trapped by 4 at the predetermined level.The output of the condenser 2 is also connected via a cut-off valve 5 in the form of a relay valve or other on/off device to an air dryer 6 fitted with a purge valve 7. The output of the air dryer is connected to the input port of a multi-circuit protection valve 8, which supplies a plurality of reservoirs, as required for the various brake systems of the vehicle which form no part of the present invention. A governor device denoted by reference 9, senses the pressure at the input port to the multi-ciruit protection valve to provide a signal both to the on/off valve 5 and to the air dryer purge valve 7.Additionally, the condenser 2 is provided with a suitable discharge valve la operable by a further governor 11,which senses the pressure at the input to the single circuit protection valve 4 the governor 11 being set to a pressure level which is substantially higher than the pressure level to which the governer 9 is set.

In operation of the system of Fig. 1, the compressor which is driven by the vehicle engine supplies compressed air via the condenser 2 and the normally open valve 5 to the input to the air dryer 6. During passage of air through the air dryer 6 the air flows through desiccant and emerges as a dry air supply to the multi-circuit protection valve 8 for charging the respective reservoirs of the braking system. Dry air is highly desirable for this because the valves and other components in the system are otherwise susceptible to freezing or maloperation due to the presence of condensed moisture and other contaminants which can be removed by the air dryer.

The air dryer is more or less a conventional device which is arranged to be purged from time to time for the purposes of regenerating the desiccant as referred to previously. Such purging in the present example is achieved by the pressure in the output line to the multi-circuit protection valve 8 attaining a predetermined pressure. Typically this pressure may be 120 psi., at the same time as initiating the purge, the governor 9 causes the valve 5 to shut off thereby interrupting the flow of air into the air dryer from the compressor However, since the condenser 2 is connected between the compressor 1 and the cut-off valve 5, compressed air can continue to flow via the condenser and the protection valve 4 into the reservoir 3, such air being usable for operating items of auxiliary equipment such as windscreen wipers.In the event of the output of the compressor exceeding the demand for air from the reservoir 3, the pressure at the output of the condenser progressively rises and if this reaches a pre-determined higher value, typically 140 psi, before the governor 9 signals the cutoff valve 5 to re-open, a dump valve 10 of the condenser is operated to both vent the output of the compressor and to discharge any accumulated condensate within the condenser 2.

In a modification, the governor 9 may incorporate or be replaced by a timer or other device which can initiate operation of purge valve 7 and cut-off valve 5 at suitable intervals to ensure air dryer purging occurs. Such timer or device may be electronic.

By virtue of the provision of an additional pressure vessel, such as reservoir 3, connected between the compressor and the cut-off valve 5, it will be appreciated that the compressor can be permitted to continue to operate during purging of the air dryer 6. Accordingly, since compressor operation is not interrupted during purging, the optimum charging capacity of the compressor can be utilised in a relatively simple and inexpensive manner.

Referring now to Fig. 2 of the drawings, the arrangement is substantially identical to that of Fig. 1 with the exception that the reservoir 3 is now provided with a control valve 21 which may be a control valve of an air-operated tool. The output side of this control valve 21 is connected as one input to a double check valve via the other input of which the output signal from the governor 9 is now connected to the cutoff valve. By such means, a purge cycle of the air dryer 6 can be initiated either by the governor 9 or by operation of the control valve 21, from a closed state to an open state, which occurs from time to time during the normal use of the vehicle. If, therefore, the demand for air for brakes has been excessive, the operation of auxilliary tools fed from reservoir 3 has the effect of ensuring that the air dryer is purged.Otherwise, the system operates in a manner which is identical to the above described operation of Fig. 1. Equally, air tool operation would not cause flooding of the air dryer desiccant irrespective of time of useage.

If the vehicle is fitted with an air-operated door such as may be provided on a passenger bus, a pressure signal may be provided to the double check valve 22 of Fig. 2 by operation of the doors and, of course, other auxilliaries may be directly connected to the reservoir 3 for more or less continual operation.

With the system described in connection with Figs. 1 and 2, it will be appreciated that the condenser 2 is only vented to dispel accumulated moisture when the system reaches the relatively higher pressure setting of the governor 11. If the demand for compressed air from the system is particularly high, this could mean that the condenser is too rarely purged of accumulated moisture. The valve may be provided in such a case with means for operating it manually or electronically from time to time-or, alternatively or additionally, an arrangement such as shown in Fig. 3 could be adopted.

In the arrangement of Fig. 3, a suitable pressure responsive two-position control valve denoted by reference 31, is incorporated in the connection between the governor 11 and the valve 10 which purges the condenser. A control pressure to the valve 31 is derived from the output of the manually operable valve 31 such that when the control valve 31 is not operated and reservoir 3 is disconnected from the output line. The valve 31 has an unoperated position in which the valve 10 can receive a control signal from the governor 9 at the same time as the air dryer receives a purge signal. In the alternative condition when the valve 31 is operated, the system reverts to a manner or operation which corresponds to the manner of operation of Fig.

2.

Whilst in the foregoing description of embodiments of the invention, the cut-off valve 5 is a separate valve the air dryer 6 may be provided with an integral input cut-off valve which is incorporated in the air dryer to operate -with the purge valve.

Such an air dryer is described in more detail in the specification of copending United Kingdom Patent Application No. 8815796.1.

Other variations and adaptations of the inventionmav be made and it will be appreciated that substantially greater advantage is thereby enabled to be taken of the output capacity of a compressor even when an air dryer with a single desiccant chamber is included in the charging path to storage reservoirs.

Claims (9)

1. A compressed gas system including a gas compressor connected to a reservoir or utilisation means via a cut-off valve and gas drying means responsive to a control signal from time to time to close the cut-off valve and to initiate regeneration of the gas drying means a compressed gas storage vessel being connected to a point between the compressor and the cut-off valve and into which vessel compressed gas can thereby flow from the compressor whilst the cut-off valve is closed.

2. A compressed gas system as claimed in claim 1 including a condenser included in the flow path between the compressor and the cut-off valve and means operable to discharge condensate therefrom when the fluid pressure in said flow path exceeds a first predetermined pressure valve.

3. A compressed gas system as claimed in claim 1 or 2 including a compressed gas storage reservoir connected at said point via a pressure protection valve.

4. A compressed gas system as claimed in claim 3 including a further valve in an output connection from said storage reservoir and means for applying a said control signal when said further valve is operated from one state to another state.

5. A compressed gas system as claimed in claims 2 and 3 including a further valve in an output connection from said storage reservoir and said means operable to discharge condensate from the condenser when said further valve is operated from one state to another state.

6. A compressed gas system as claimed in claim 1, 2, 3, 4 or 5, wherein a governer is included responsive to output pressure of the gas drying means exceeding a further predetermined pressure valve.

7. A compressed gas system as claimed in claim 2, or claim 3,5 or 6 when dependent on claim 2, said means operable to discharge condensate including a dump valve comprising

8. A compressed gas system as claimed in claims 6 and 7 wherein said dump valve operates at a said predetermined first pressure valve higher than the said further predetermined pressure valve.

9. A compressed gas system substantially as described herein with reference to Fig. 1, Fig. 2 or Fig. 3 of the accompanying drawing.