Pumps – Processes
Reexamination Certificate
2001-04-09
2003-04-29
Freay, Charles G. (Department: 3746)
Pumps
Processes
C417S383000, C417S395000
Reexamination Certificate
active
06554578
ABSTRACT:
The invention relates to a diaphragm pump with a device for controlling the position of a diaphragm, which separates a conveying chamber from a displacement chamber, and with a reservoir for the hydraulic medium, which is in connection with the displacement chamber viva refilling unit.
The invention moreover relates to a method for controlling a diaphragm, which separates the conveying chamber from the displacement chamber of a diaphragm pump and which is driven by an oscillating displacer by means of a hydraulic medium, wherein the displacement chamber is resupplied with hydraulic medium via a line as needed.
Pumps of this type are known in the form of a piston diaphragm pump-from EP A1 0 085 725. The piston diaphragm pump has a displacement piston, which is oscillatingly moved back and forth in a displacement chamber, which is completely filled with a hydraulic medium. Because of this, the diaphragm arranged between the conveying chamber and the displacement chamber performs a diaphragm stroke, which corresponds to the volume of the piston stroke.
During the intake stroke, the fluid to be conveyed flows into the conveying chamber via the inlet valve, and is expelled via the head valve during the pressure stroke.
In most cases, a support plate, which can be displaced over a limited range, is provided in the displacement chamber and protects the diaphragm against an excessive deflection toward the end of the intake stroke.
If, after a defined period of operation, the inevitably occurring losses of hydraulic medium lead to the diaphragm position at the end of the intake stroke being slowly displaced toward the displacement chamber, the diaphragm arrives at the support plate or at a plunger, which senses the diaphragm position. The support plate or the plunger are displaced by the diaphragm against the pressure of springs in the direction toward the displacement work chamber. The plunger, which senses the diaphragm position directly, or the support plate, mechanically unblock a refilling valve in the process, which is opened because of the underpressure prevailing in the displacement work chamber and permits hydraulic medium to flow from a reservoir into the displacement work chamber. In the course of this, the diaphragm and the support plate again move under the pressure of the springs in the direction toward the conveying chamber. During the course of this movement the closure device of the refilling valve also slides again in the direction toward the conveying chamber and closes the refilling valve.
An impairment of the conveying properties of the diaphragm pump can arise as a result of the expulsion of air originally dissolved in the hydraulic medium. In such cases it is necessary to permit a volume to escape from the displacement chamber. A so-called venting valve is provided for this purpose, which makes possible the escape of excess amounts of hydraulic medium or released air. In the course of the initial operation of a diaphragm pump, or of a change of the set stroke length of the connected pump operating unit, the venting valve is simultaneously used to remove excess amounts of hydraulic medium from the displacement chamber in order to assure the function of the mechanical refilling device.
Such a venting valve is known, for example, from the company publication “AREX” of Applicant.
The direct determination of the limit positions of the diaphragm by means of an electronic sensor as a replacement for the mechanical determination of the instantaneous diaphragm location has been proposed in EP B1 0 607 308. The electronic signal of the position sensor is compared with a predetermined maximum value in a control unit. In case the maximum value is exceeded, a signal for opening a refilling valve is generated, which prevents an overload of the diaphragm. The disadvantage of this previously known solution lies in that a mass-containing magnet, whose magnetic field is required by the electronic sensor for detecting the location of the diaphragm, must be attached to the diaphragm for detecting the position of the diaphragm. The uneven mass distribution on the diaphragm required for this can lead to locally increased loads, which disadvantageously reduces the service life expectancy of the diaphragm. Because of the omission of a diaphragm stop, or support plate, on the displacement chamber side, refilling the hydraulic chamber in case of an operation at an admission pressure in the suction line, which lies above the pressure of the ambient air, is only possible if, by means of an additional pressure generator, the amount of hydraulic fluid to be replaced is brought to a somewhat slightly higher pressure than the admission pressure in the suction line In addition, the lack of the diaphragm stop can lead to an overload of the diaphragm under certain operating conditions.
Finally, a device for an electronic check of the diaphragm position in diaphragm process pumps is known from DE A1 43 36 823, wherein the position of the diaphragm is determined by means of an electromechanical or electronic transmitter and receiver. For an exact control for preventing breakage or premature wear by an overload, a signal, which controls the admission of the hydraulic medium to the displacement chamber, is generated by means of an electronic evaluation unit. An electromechanical sensor, which directly determines the position of the diaphragm by means of a spring-loaded plunger, is proposed for detecting the diaphragm position. In this case, too, the diaphragm is additionally stressed by the force of the plunger, which basically results in a reduced life expectancy of the diaphragm.
It is the object of the invention to create a diaphragm pump, wherein the volume of the displacement chamber can be checked in the simplest possible way, so that the diaphragm is treated gently and the operational dependability of the pump as a whole is increased.
This object is attained in connection with the diaphragm pump in accordance with the species in that a pressure sensor is arranged in the displacement chamber, which is connected with an evaluation unit designed for generating a refill signal, so that a refill unit is actuated by means of an operative connection. The pressure sensor located in the displacement chamber reports the creation of an underpressure during the intake stroke to the evaluation unit. There, this signal is compared, for example with a predetermined threshold value. As soon as the predetermined threshold value has been exceeded, the evaluation unit generates a signal which causes the refilling of the displacement chamber with hydraulic fluid. Overloading of the diaphragm is assuredly prevented in this way. The threshold value can be easily adapted to various operating conditions. Since the pressure sensor has no movable parts, the operational dependability is advantageously increased in comparison with mechanical systems. The diaphragm is not additionally stressed by the pressure sensor, since the latter is not in direct contact with the diaphragm and instead only comes into contact with the hydraulic medium.
Thus, the invention is based on the electronic evaluation of the chronological course of pressure in the displacement chamber of a hydraulically controlled diaphragm pump. Also, a selective allocation of this course of the pressure to the displacer position takes place. The correct filling of the displacement chamber is assured by means of an algorithm being run in a computer unit and by a refill unit, which is actuated by an operative connection. Occurring leaks, or a lack of hydraulic medium in the displacement chamber, are detected and a replacement is provided again.
If a support plate for the diaphragm is arranged in the displacement chamber, an additional, more distinctive underpressure pulse is generated in the displacement chamber as soon as the diaphragm comes to rests against the support plate during the intake stroke. This underpressure pulse can be evaluated even more precisely by the evaluation unit and a signal for refilling can be generated from this, which advantageously
Baker & Hostetler LLP
Bran & Luebbe GmbH
Freay Charles G.
Gray Michael K.
LandOfFree
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