Regulation of fluid conditioning stations

Details Regulation of fluid conditioning stations Regulation of fluid conditioning stations

1998-12-17

2001-07-24

Walberg, Teresa (Department: 3742)

Pumps

With condition responsive pumped fluid control

Plural pump units with individual or relative control

C417S038000

Reexamination Certificate

active

06264435

ABSTRACT:

The present invention relates to improvements in the regulation of fluid conditioning stations which include a plurality of pumping devices, at least one fluid accumulator container, at least one pressure transducer and regulating means, the conditioning station providing a fluid at a certain pressure and flow for consumption, the pumping devices starting and stopping so that the pressure at the measuring point is maintained between two pressure-limit values called start pressure, which is determined in function of a limiting value to be maintained, and stop pressure.
The term “pumping device” is used in this specification both to designate the devices which work with positive pressure, such as compressors, and to designate devices which work with negative pressure, for example “vacuum pumps”.
The term “hysteresis” is used to designate an interval between two pressures, for example between the start pressure and the stop pressure of a pumping device.
In this specification the term “fluid conditioning stations” is used particularly, though not exclusively, to designate both compressor stations which work at constant intake pressure and variable output pressure, and the so-called vacuum stations, which normally work under a regime of variable intake pressure and constant outlet pressure.
The conditioning stations have the function of transmitting power by conditioning the variables, such as pressure and flow.
The invention also relates to improvements in the regulation of stations which condition other variables such as temperature and flow of a fluid, such as water or thermal oil.
BACKGROUND OF THE INVENTION
Traditionally, in fluid conditioning stations the pumping devices are started and stopped in such a way that the pressure in the fluid accumulating container(s) is kept between two pressure limiting values, called start pressure, which is determined in function of minimum values to be maintained, and stop pressure which is determined in function of the maximum recommendable number of starts per unit of time of the pumping devices.
Said stations presented the disadvantage of not adapting well to consumption, which is random and can vary across wide values. One example of variable consumption is to be found in hospitals, in which consumption is maximum in the mornings of working days (due to an increase in operating and resuscitation theatres in use) and minimum on Saturdays and Sundays and particularly in the month of August. The ratio between maximum consumption and minimum consumption can easily be 5 to 1.
In these cases, the starting and stopping of the pumping devices took no account at all of the possibility of adapting the station to consumption, so that, for example, a high-power pumping device could be started up for a small consumption flow.
This system involved a considerable squandering of energy and high wear of pumping devices, which resulted in shorter pump life.
Moreover, the flow supplied by the station was not suitably controlled, since the most suitable combination of pumping devices was not always in operation.
Spanish patent application P9300399 by the same applicants suggested several solutions for the aforesaid problems.
Essentially, said application is characterized in that only one pumping device is put into operation when the pressure in the fluid accumulator containers reaches or exceeds the start pressure value and/or when the flow provided by the pumping devices which are operating is lower than the consumption flow; and only one pumping device stops when the pressure in the fluid accumulator containers reaches the stop pressure value and/or when the flow provided by the pumping devices which are operating exceeds the consumption flow.
This feature allowed a stepped increase of the flow provided by the station to be ensured, in as many steps as there were pumping devices making up peak flow at the station in question, together with progressive adaptation to changing consumption.
The aforesaid patent application also suggests other possibilities for controlling stopping of the pumping devices by means of conditions such as a number of starts/stops per unit of time, or by fixing a cycle during which there can be no stoppage. Also suggested as an alternative to stopping a pumping device which can operate without pumping (“stand by”).
DESCRIPTION OF THE INVENTION
The present invention manages to improve the energy saving of the station and also to improve the operating conditions of the pumping devices.
According to one embodiment, when the start pressure is determined in function of a limiting value to be maintained, the improvements of the invention in the regulation of fluid conditioning stations are characterized in that when the pressure at the measuring point reaches or exceeds the start pressure value and/or when the flow provided by the pumping devices which are in operation is less than the consumption flow, the flow provided by the station increases by one step, and when the pressure at the measuring point reaches the stop pressure value and/or when the flow provided by the pumping devices which are in operation exceeds the consumption flow, the flow provided by the station reduces by one step.
In this description, “step” is taken to mean the flow of one pumping device of a station or the difference of flows between two sets of pumping devices of a station.
The steps are thus not limited to a single pumping device, so that improved energy saving is achieved.
Advantageously, when one pumping device stops and another starts up in the sense of increasing the total capacity of the station (where there exist at least two different flow rates from pumps), stoppage of the first does not take place until the set of pumping devices has reached or exceeded the start value by a certain percentage. The response speed is thus increased, which means that the time during which the pressure is below the start value is reduced.
The regulation of fluid conditioning stations can also be improved if the pressure measuring point(s) are situated at the ends of the various consumption lines, or if the pressure measuring point(s) are situated at a point between the consumption points and the filters of the fluid conditioning station, taking in both cases the signal(s) from the most unfavourable measuring points or a combination of measuring points.
The usefulness of these solutions becomes clearer if they are compared with the conventional solution.
If a hospital vacuum station takes as a starting parameter a necessary pressure of −400 mm Hg at the end of the line, and the most unfavourable case is taken to be a pressure loss in filters (maximum dirtiness at nominal flow) and line (maximum loss at nominal flow) of 50 mm Hg, and if on the other hand the real pressure loss is 10 mm Hg at each position, then the following values would obtain:
In the conventional case, in which the pressure measuring points are in the station, the start pressure would be 500 mm Hg and the real pressure at the end of the line 480 mm Hg, since 480=500−10−10.
According to a first embodiment of the invention, in which the pressure measuring points are at the ends of the various lines, the start pressure would be 420 mm Hg at the station, since 420=400+10+10, and the real pressure at the end of the line 400 mm Hg, which is the preselected pressure.
According to a second embodiment, in which the pressure measuring points are at a point which is between the consumption points and the filters of the station, the start pressure would be 460 mm Hg at the station, since 460=450+10, and the real pressure at the end of the line 440 mm Hg, since 440=450−10.
From this it can be deduced that the closer the pressure measuring points are to the consumption points the greater will be the energy saving.
In the two embodiments described, in which the sensors are situated at a certain distance from the station, the start pressure depends upon the measuring point, so that adjustments could be considered to be floating, that is, they depend u

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