A hydraulic nut incorporates its own internal hydraulic jack. This enables large diameter bolts to be tensioned with ease to high and accurate pre-loads.Hydraulic nuts are widely used in the oil and gas, offshore, mining, conventional & nuclear power generation, and heavy equipment industries on applications including:
Titan hydraulic nuts are available in four types and a wide range of sizes, the largest ever made being in excess of 20 inch thread size. Typically, they range from M24 to M250. Hydraulic nuts are available in standard and custom designs. All nuts are made to order, so manufacturing a custom-built nut to suit the application is common.Advantages
- Even and accurate pre-load
- Low loss of initial load (shim type)
- No torque or torsional stress
- No flogging hammers or spanners
- Self-aligning (shim type)
- Improved fatigue performance
- Long life of internal jack
- Ideal for confined spaces
Hydraulic nuts are quickly installed. A hydraulic pump activates the internal jacking system, so the effort required to tighten a very large diameter bolt is reduced to the effort needed to operate the pump. If an air driven pump is used, the tightening operation is fast and effortless.
Normally spanners, flogging hammers, or torque wrenches are required to tighten large bolts, but these are not required when a hydraulic nut is used. They also induce high torsional stresses in the bolt during tightening and can damage the bolt threads. As there is no nut rotation during tightening a hydraulic nut, the operation can be performed in a confined space and torsional stresses or thread damage are eliminated.
The nut develops a load which is directly proportional to the oil pressure. This can be accurately controlled and because it is developed hydraulically, it is evenly applied. Any number of hydraulic nuts can be connected together for simultaneous operation. In this way, all of the bolts in a joint can be evenly loaded to the same high and accurate pre load.
When the oil pressure is applied, the joint is compressed and the bolt stretches. This produces a gap between the body of the nut and the piston. Depending on the type of nut, either shims are inserted into the gap, or a locking collar on the piston is turned. When the hydraulic pressure is released, the load is transferred onto the shims or the locking collar to retain the load.
When tightening bolts it is possible to induce bending stress in the shank of the bolt if the joint faces are not true or flange rotation occurs in a flanged joint. The hydraulic nut is self aligning. Therefore under pressure, misalignment or flange rotation it will produce a variation in the gap between the nut body and the piston. In the case of shim type nuts, tapered shims can be made and fitted to eliminate the effects of misalignment and flange rotation. In the case of collar type nuts, a spherical washer would need to be fitted under the hydraulic nut.
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