Pumps – Motor driven – Relatively movable pumping members driven by relatively...
Patent
1996-01-05
1997-06-03
Gluck, Richard E.
Pumps
Motor driven
Relatively movable pumping members driven by relatively...
417344, 417346, F04B 910, F04B 4906
Patent
active
056347790
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The instant invention relates to reciprocating linear motion piston pumps, driven by hydraulic fluid, referred to hereinafter as pumps or pumping machines.
PRIOR ART
Predominantly, two-piston pumping machines are in use, although one-piston and three-piston pumps also exist. Such pumps are employed for the pumping of concrete and other difficult to move materials. These are the only pumps capable of moving such materials at high pressures.
The present technology uses long piston strokes, mostly in the neighborhood of 2 meters, in order to lengthen cylinder life, especially when abrasive materials are pumped.
In two-piston machines, the advance of one of the two pistons causes the other piston to return, by means of displacing into the other cylinder, behind its piston, the hydraulic fluid contained in the chamber formed by the cylinder wall, the piston rod, the piston's back and the rod gland (bushing, sealing the rod's exit from the hydraulic cylinder to the "material" or "pumping" cylinder). This mechanism operates with equal advance and return piston speeds. The simultaneous arrival of the advancing and returning pistons to their respective end and beginning points of the stroke implies a short interruption in the pump's flow at the end of each stroke.
This is corrected, in one existing design, at the expense of an additional hydraulic circuit which slowly closes the advancing piston's hydraulic fluid admission valve as the other piston's admission valve is being opened.
The problem of pulsations, i.e. the additional variation in the pump's delivery flow due to the unavoidable compression of the long column of material in the material cylinder being pumped at the beginning of each stroke, is solved, in one existing design, by adding a third cylinder. As one of the three pistons advances, the second piston returns and the third piston precompresses its column.
U.S. Pat. No. 3,662,652 discloses a hydraulic pump as set out in the pre-characterizing part of claim 1, having at least three power cylinders in fluid communication with one another and which are operable in a cycle with suction, precompression and discharge phases.
The main shortcomings of the available technology are:
a) The presently available designs imply the need for as many sizes of the machine as there might be different flow requirements. This means that many different size components have to be manufactured and stocked.
b) The known machines are integral units and any maintenance requires stopping the pumping operation until the machine is repaired.
c) The means employed to eliminate variations in the machine's flow (pulsation) require an additional hydraulic circuit and a third cylinder, involving complex design and considerable additional cost.
d) The long strokes adopted lead to radial stresses on the piston, the rod, the bushing and the cylinder walls. These stresses, to date, have been unavoidable and are due to even the slightest deviation of the hydraulic and pumping cylinders' axis. The phenomenon, sometimes referred to as piston blocking, causes premature cylinder, rod, piston guides and bushing wear, and is responsible for an important loss in mechanical efficiency.
e) The hydraulic fluid valves employed (mainly when fixed displacement hydraulic pumps are used to drive the machine) are either conventional, directional spool valves or the so-called two-way directional logic element, cartridge valves. In the first case, considerable pressure drops are present, which are inherent in the spool valve design. In the second case, pressure drops are present due to the spring closing the valve.
f) When the machines are used to pump materials that can be handled by disk valves, disk valves of conventional design are used. Since these valves were originally designed to be used in mechanical piston or plunger pumps at much higher closing speeds, they cause an unduly high pressure drop in the hydraulically driven piston pumps, where more closing time is available. In such pumps, specially designed disk valves shou
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patent: 3981622 (1976-09-01), Hall et al.
patent: 3994627 (1976-11-01), Calzolari
patent: 4470771 (1984-09-01), Hall et al.
patent: 4490096 (1984-12-01), Box
patent: 4555220 (1985-11-01), Hall et al.
FDP Engineering SA
Gluck Richard E.
Lobo Alfred D.
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