Hydraulic bolt tensioner

Abstract: A hydraulic bolt tensioner having a first chamber (5) and a second chamber (12), a hollow first piston (6,7) movable in the first chamber (5) and partially extending into the second chamber (12), a second piston (9,10) displaceable inside the first piston (6,7) and movable in the second chamber (12), the second piston (9,10) having connecting means (11) for connecting with an end of a bolt (17), and a hydraulic fluid supply for supplying hydraulic fluid into the first chamber (5) so that, when hydraulic fluid pressure is applied to the first chamber (5), the first piston (6,7) moves so that the first piston displaces the hydraulic fluid in the second chamber and moves the second piston (9,10) to pull the end of the bolt.

Description: This invention relates to hydraulic bolt tensioners. Hydraulic tensioners are widely known and utilized. It is desirable to design such a hydraulic tensioner which has a relatively low power consumption. In connection with this a hydraulic tensioner has been proposed in W094/14578 having a bolt pulling means which includes an engaging element arranged to engage the end of the bolt, fluid operated means formed by a plurality of cylinders arranged on top of one another along the axis of the engaging element and having cylinder chambers, and a plurality of pistons axially movable in the cylinder chambers. The cylinder chambers and the pistons movable in them are coextensive and substantially identical. The pistons simultaneously apply a pulling force to the same engaging element which pulls the bolt and a higher pulling force is generated with a predetermined power consumption from the hydraulic source or the same force applied for pulling the bolt is produced with a lower power consumption of the hydraulic source. The engaging element pulls the bolt, and additional fluid-operated means turn the nut down when the bolt is pulled to a desired load. However the bolt tensioner disclosed in W094/14578 has the disadvantage that in order to keep its diameter small, several cylinder stages are required which in turn make the bolt tensioner substantially high. While in some applications height is not important, there are other applications where the overhead clearance is limited so that the above described tensioner cannot be used. It is therefore an object of the present invention to provide a hydraulic bolt tensioner which avoids the disadvantages of the prior art. In keeping with these objects and with others which will become apparent hereinafter, there is provided a hydraulic bolt tensioner as claimed in the ensuing claim 1. When the tool is designed in accordance with the present invention, it avoids the disadvantages of the prior art and provides for the highly advantageous results. When the hydraulic bolt tensioner is designed in accordance with the present invention, with the use of a regular industrial hydraulic pump which usually provides the maximum pressure of 68,947KPA (10,000 psi), three times the pressure can be developed in an independent chamber which is connected to the bolt tensioner. The height of the tool is reduced by 50% and the diameter of the tool is equivalent to the diameter of the tool disclosed in W094/14578. An embodiment of the invention will now be described, by way of example only, with particular reference to the accompanying drawing, the sole figure of which is a view showing a hydraulic bolt tensioner in accordance with the present invention. A hydraulic bolt tensioner in accordance with the present invention has a housing which is identified as a whole with reference numeral 1. The housing 1 is hollow and has a stepped inner opening with a first opening portion 2 and a second opening portion 3 separated from one another by an inwardly projecting partition 4. A first substantially cylindrical hydraulic chamber 5 is formed in the region of the opening portion 2. First piston means cooperate with the first hydraulic chamber 5 and include a tubular first piston 6 which is axially displaceable in the first chamber 5, and an elongate axially extending tubular piston extension 7. The first piston means 6, 7 are hollow and have an inner opening 8. Second piston means include a piston 9 which is axially displaceable in the opening portion 3 and an elongate axially extending piston rod 10 which is axially displaceable in the opening 8 of the first piston means. The second piston means, or in particular the piston rod 10 of the second piston 9, has a central opening 11 provided with a thread for engaging with a thread of a bolt to be tensioned. A second substantially cylindrical hydraulic chamber 12 is formed substantially between the first piston means and the second piston means. As can be seen from the drawing, the second hydraulic chamber 12 is formed between the piston rod 7 of the first piston means 6, 7 and the piston 9 of the second piston means 9, 10. The second cylinder chamber 12 is filled with oil through passages 13 which after filling can be closed by a filler plug or bolt 14. The first cylinder chamber 5 during operation is supplied with a hydraulic fluid from a hydraulic source, for example from a regular industrial hydraulic pump, through a supply passage 15. A nut turning portion of the tool is identified as a whole by reference numeral 16 and operates for turning the nut applied on the bolt. The nut turning portion 16 can be formed completely identically to the nut portion disclosed in W094/14578 or in any other way. The tool in accordance with the present invention operates in the following manner: When the hydraulic fluid is supplied from the hydraulic fluid source to the first chamber 5, the first piston 6 is displaced and its tubular piston extension 7 displaces the hydraulic fluid in the secondary chamber 12. Thereby the second piston 9 with the piston rod 10 is displaced and pulls the end of a bolt 17. While the invention has been illustrated and described as embodied in a particular hydraulic bolt tensioner, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the present invention as defined in the ensuing claim 1.

Claims: A hydraulic bolt tensioner comprising means forming a first chamber (5) and a second chamber (12), first piston means (6,7) comprising a hollow first piston (6) and a hollow first piston rod (7), the first piston (6) being slidably received in said first chamber (5) and the first piston rod (7) extending partially into said second chamber (12), second piston means (9,10) comprising a second piston (9) movable in said second chamber (12) and a second piston rod (10), and means (15) for supplying hydraulic fluid into said first chamber (5) for moving said first piston means (6,7), characterised in that the second piston rod (10) is slidably received in said first piston means (6,7), is connected at one end to the second piston (9) and has, at an opposite end, connecting means (11) for connecting with an end of a bolt (17), in that the second chamber (12) is closed at one axial end by the first piston rod (7) and at its opposite axial end by the second piston (9), and in that, seen in the axial direction, the area of the first piston (6) subjected to pressure of hydraulic fluid in the first chamber (5) and the area of the second piston (9) subjected to pressure of hydraulic fluid in the second chamber (12) each exceeds the area of the first piston rod (7) subjected to pressure of hydraulic fluid in the second chamber (12), whereby when hydraulic fluid pressure is applied to said first chamber (5), said first piston means (6,7) moves so as to displace the hydraulic fluid in said second chamber (12) and move said second piston means (9,10) to pull the end of the bolt (17). A hydraulic bolt tensioner according to claim 1, characterised in that it further comprises a housing (1), said first chamber (5) being formed between said housing (1) and said first piston means (6,7).

Inventors: JUNKERS JOHN K, JUNKERS, JOHN K.
Applicants: JUNKERS JOHN K, JUNKERS, JOHN K.
Application year: 1995
Main classification: B25B29
IPC codes: B25B29, G21C13, B25B21, F16B31, B23P19