GB2155104A - A jack incorporating a fluid sac - Google Patents

Abstract

A jack includes a high pressure chamber (1), a fluid sac (2) acting as a low pressure chamber and a pump (4) for pumping a working fluid of the jack from the fluid sac (2) into the high pressure chamber (1). The fluid sac (2) is of rubber thus expanding and contracting as fluid is returned to it or drawn from it, and so avoiding the need for air entering the hydraulic circuit of the jack which would diminish its lifting capacity. <IMAGE>

Description

SPECIFICATION Jack The present invention relates to a hydraulic jack.

The known jacks vary extremely but their internal structures usually include two chambers, namely, a high pressure chamber and a low pressure chamber. The working and function thus obtained is well known to those skilled in this art and will no more be described. A typical known jack, as shown in Fig. 1, has a high pressure chamber a and a low pressure chamber b. The small black triangles in the lower part of the drawing are the welds. The welding procedure for the jack is necessary because a fluid tight condition for the working fluid of the jack must be maintained. But it is necessary to allow air into the low-pressure side of the circuit since otherwise a vacuum (negative pressure) region will be formed in low pressure chamber b when fluid is withdrawn.The air causes the following problems: first, the air mixed within the liquid is inclined to choke the liquid passage while pumping. Second, when the air is carried into the high pressure chamber the jack will suffer a poorer lifting capacity since the compressibility of the air is far greater than that of the liquid. The above problem is apt to be seen when the jack is laid on its side and then put into use. The invention aims to alleviate these shortcomings.

According to the present invention, a jack incorporating a high pressure chamber, a low pressure chamber and a pump for pumping a working fluid of the jack from the low pressure chamber into the high pressure chamber is characterized in that the low pressure chamber is a fluid sac which is expandible. Preferably the jack further comprises a shell for shielding the fluid sac.

Generally, the jack has a base portion and the shell can be threadedly engaged with the base portion. The fluid sac can be made of rubber or like material.

The present invention may best be understood with reference to the accompanying drawings, in which: Fig. 1 A is a partially sectional view of a typical embodiment of the known jacks; Fig. 1 B is a partially sectional view of the pump portion of the jack in Fig. 1; Fig. 2A is a partially sectional view of a preferred embodiment of a jack incorporating a fluid sac of the present invention; Fig. 2B is a partially sectional view of the pump portion of the jack in Fig. 2A; Fig. 3A is a partially sectional view of another preferred embodiment of a jack incorporating a fluid sac of the present invention; and Fig. 3B is a partially sectional view showing the jack in Fig. 3A taken from a different direction.

Referring now to Figs. 2A and 2B, there is shown a preferred embodiment of a jack incorporating a fluid sac which includes a high pressure chamber 1, a fluid sac 2 acting as a low pressure chamber, a crown or ram 3, a pump portion 4 and a base portion 5. Fluid sac 2 is connected to pump 4 by a pipe 41 and through a release valve 43 to high pressure chamber 1 by another pipe 42. The working of such a jack is no different from the known one except that the sac 2 expands or contracts as fluid passes to or from it, and thus will not be further described. The small, black triangles in the drawing represent welds and it can be seen that a shell 21 for fluid sac 2 need not be welded together with a base 5 of the present jack since the space 22 for the fluid sac 2 does not need to be absolutely tight.Accordingly, a simplified engagement, e.g. a threaded engagement between shell 21 and base 5 is deemed enough.

Fluid sac 2 is designed to be expansible so that the working fluid sucked therefrom will contain no air and high pressure chamber 1 will be free of any air which would cause poorer lifting capacity. Fluid sac 2 can be made of rubber, e.g. NBR. Such a jack incorporating a fluid sac thus can be expected to be an improvement over the known jacks.

Another embodiment of the present invention is shown in Figs. 3A and 3B which can be readily recognized by one skilled in this art.

1. A jack having a high pressure chamber, a low pressure chamber and a pump for pumping a working fluid of said jack from said low pressure chamber into said high pressure chamber characterized in that said low pressure chamber is an expandiblefluid sac.

2. A jack incorporating a fluid sac according to claim 1 characterized in that said jack further comprises a shell for shielding said fluid sac.

3. A jack incorporating a fluid sac according to claim 2 characterized in that said jackfurther includes a base portion and said shell is threadedly engaged with said base portion.

4. Ajack incorporating a fluid sac according to claim 3 characterized in that said fluid sac is made of rubber.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Jack The present invention relates to a hydraulic jack. The known jacks vary extremely but their internal structures usually include two chambers, namely, a high pressure chamber and a low pressure chamber. The working and function thus obtained is well known to those skilled in this art and will no more be described. A typical known jack, as shown in Fig. 1, has a high pressure chamber a and a low pressure chamber b. The small black triangles in the lower part of the drawing are the welds. The welding procedure for the jack is necessary because a fluid tight condition for the working fluid of the jack must be maintained. But it is necessary to allow air into the low-pressure side of the circuit since otherwise a vacuum (negative pressure) region will be formed in low pressure chamber b when fluid is withdrawn.The air causes the following problems: first, the air mixed within the liquid is inclined to choke the liquid passage while pumping. Second, when the air is carried into the high pressure chamber the jack will suffer a poorer lifting capacity since the compressibility of the air is far greater than that of the liquid. The above problem is apt to be seen when the jack is laid on its side and then put into use. The invention aims to alleviate these shortcomings. According to the present invention, a jack incorporating a high pressure chamber, a low pressure chamber and a pump for pumping a working fluid of the jack from the low pressure chamber into the high pressure chamber is characterized in that the low pressure chamber is a fluid sac which is expandible. Preferably the jack further comprises a shell for shielding the fluid sac. Generally, the jack has a base portion and the shell can be threadedly engaged with the base portion. The fluid sac can be made of rubber or like material. The present invention may best be understood with reference to the accompanying drawings, in which: Fig. 1 A is a partially sectional view of a typical embodiment of the known jacks; Fig. 1 B is a partially sectional view of the pump portion of the jack in Fig. 1; Fig. 2A is a partially sectional view of a preferred embodiment of a jack incorporating a fluid sac of the present invention; Fig. 2B is a partially sectional view of the pump portion of the jack in Fig. 2A; Fig. 3A is a partially sectional view of another preferred embodiment of a jack incorporating a fluid sac of the present invention; and Fig. 3B is a partially sectional view showing the jack in Fig. 3A taken from a different direction. Referring now to Figs. 2A and 2B, there is shown a preferred embodiment of a jack incorporating a fluid sac which includes a high pressure chamber 1, a fluid sac 2 acting as a low pressure chamber, a crown or ram 3, a pump portion 4 and a base portion 5. Fluid sac 2 is connected to pump 4 by a pipe 41 and through a release valve 43 to high pressure chamber 1 by another pipe 42. The working of such a jack is no different from the known one except that the sac 2 expands or contracts as fluid passes to or from it, and thus will not be further described. The small, black triangles in the drawing represent welds and it can be seen that a shell 21 for fluid sac 2 need not be welded together with a base 5 of the present jack since the space 22 for the fluid sac 2 does not need to be absolutely tight.Accordingly, a simplified engagement, e.g. a threaded engagement between shell 21 and base 5 is deemed enough. Fluid sac 2 is designed to be expansible so that the working fluid sucked therefrom will contain no air and high pressure chamber 1 will be free of any air which would cause poorer lifting capacity. Fluid sac 2 can be made of rubber, e.g. NBR. Such a jack incorporating a fluid sac thus can be expected to be an improvement over the known jacks. Another embodiment of the present invention is shown in Figs. 3A and 3B which can be readily recognized by one skilled in this art. CLAIMS

1. A jack having a high pressure chamber, a low pressure chamber and a pump for pumping a working fluid of said jack from said low pressure chamber into said high pressure chamber characterized in that said low pressure chamber is an expandiblefluid sac.

2. A jack incorporating a fluid sac according to claim 1 characterized in that said jack further comprises a shell for shielding said fluid sac.

3. A jack incorporating a fluid sac according to claim 2 characterized in that said jackfurther includes a base portion and said shell is threadedly engaged with said base portion.

4. Ajack incorporating a fluid sac according to claim 3 characterized in that said fluid sac is made of rubber.