HN Precision-Preload Stroke-Indicating Hydraulic Nut

The HN precision-preload stroke-indicating hydraulic nut provides a compact and self-contained hydraulic tensioning solution that is permanently integrated into the bolted joint, eliminating the need to remove and reinstall a separate tensioner tool for every tightening or re-tensioning operation. Once installed, the hydraulic nut can be pressurized directly using a hydraulic pump connection to apply and verify precise pre-load, making it particularly efficient for joints that require periodic retensioning or where access for external tooling is restricted.

A built-in stroke indicator allows operators to measure and monitor the actual elongation being applied to the bolt in real time during the tensioning process, providing direct control over pre-load magnitude and enabling accurate verification against design specifications. Pre-load accuracy of ±3% is achievable, significantly exceeding the repeatability possible with torque-based methods. The corrosion-resistant surface treatment protects the nut in long-term installation conditions including outdoor, marine, and chemically challenging environments.

Multiple hydraulic nuts can be pressurized and operated simultaneously from a shared pump supply, enabling synchronized full-circle clamping on flange joints to achieve uniform gasket compression and sealing performance. The HN is suitable for applications where the permanence and accessibility of a hydraulic tensioning device at the joint location offers operational or safety advantages, including large pressure vessel closures, wind turbine pitch and yaw bearing bolts, and large rotating machinery where retensioning intervals are scheduled throughout the service life.