Pumps – Expansible chamber type – Having additional chamber intake connection from nonpumping...
Patent
1988-11-21
1990-05-08
Smith, Leonard E.
Pumps
Expansible chamber type
Having additional chamber intake connection from nonpumping...
417330, 417302, 417440, 417545, F04B 2104, F04B 3100
Patent
active
049233734
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a hydraulic single piston pump for manual operation having a cylinder, a piston dividing the cylinder into a piston chamber and a rod chamber and movable power stroke and in a return stroke, and first and second channels extending through the piston from the piston chamber to the rod chamber. A check valve controls fluid flow through the first channel and opens during the return stroke.
BACKGROUND OF THE INVENTION
According to known manual pumps of this type, the passage of hydraulic fluid through the second channel is automatically controlled by means of a control valve in this second channel. The valve in the second channel opens at the beginning of each power stroke when the predetermined level of pressure in the piston chamber is exceeded, so that pressure compensation occurs continuously between the piston chamber and the rod chamber. The effective pump surface is thereby reduced to the size of the rod surface. The force being exerted on the piston with the power stroke is then automatically reduced as soon as the aforementioned limit value is exceeded. Because of this, the use of a two-stage pump has been recently discussed, which can be used in lift trucks, whereby the loads are to be lifted with as few as possible pump cycles.
SUMMARY OF THE INVENTION
The object of the present invention is to improve a single piston pump of the aforementioned type.
This object is attained by means of a hydraulic single piston pump for manual operation, comprising a cylinder, and a piston dividing the cylinder into a piston chamber and a rod chamber. The piston is movable to decrease the piston chamber in a power stroke and to increase the piston chamber in a return stroke. A first channel extends through the piston from the piston chamber to the rod chamber. A check valve is in and controls fluid flow through the first channel, and opens during the return stroke of the position. A second channel extends through the piston from the piston chamber to the rod chamber. The second channel has means for automatically controlling hydraulic fluid flow from the piston chamber to the rod chamber dependent on differential pressures in the chambers. The means includes a first choke bore along at least part of a length of the second channel.
The choke bore in the second channel reduces the costs of operation. It also leads to a reduced susceptibility to the incidence of trouble, even under rough operating conditions, and allows for a lower overall height of the pump. Above all, the choke bore leads to the condition wherein the power to be applied during the power stroke is dependent upon the velocity of operation, i.e., the pump velocity. Instead of a reversal of the effective piston surface outlay occurring when the predetermined limit value of the pressure in the piston chamber is exceeded or is not reached, which cannot be influenced by the user, in the pump according to the present invention, the user can adapt the operational power to be exerted on the piston to its entire possible range within the limits determined by the complete piston cross section and the reduced piston cross section, independent of the pressure in the piston chamber.
If, during the power stroke, the piston moves sufficiently slowly that complete pressure compensation between the piston chamber and the rod chamber is attained, the effective piston surface is the same as the rod surface, independent of influence exerted by the pressure level in the piston chamber. The more rapid the movement of the piston during power stroke, the greater remains the pressure differential between piston chamber and rod chamber. When the pump according to the present invention is associated for instance with a lift truck, any load independent of its size can be conveyed by ever greater pump velocity, which indeed also requires a higher power outlay, with fewer pump cycles at high velocity rather than with a lower pump velocity.
One further advantage of the solution of the problem according to the present inve
REFERENCES:
patent: 3112705 (1963-12-01), Chlebowski
patent: 4357798 (1982-11-01), Hung
patent: 4520908 (1985-06-01), Carpenter
Rothaar Stefan
Stuck Otfried
Flutec Fluidtechnische Gerate GmbH
Savio, III John A.
Smith Leonard E.
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