What is the Riverhawk “HRT” Hydraulic Rod Tensioner System?
The Riverhawk Hydraulic Rod Tensioner (HRT) (Figure 1) system is a compact, two-part tensioning device that can be readily retrofitted to existing studs and restricted footprints. The Hydraulic Rod Tensioner does not face design limitations such as temperature-limiting seals and lubricants, coatings, and coefficient of friction due to torquing.
Hydraulic Rod Tensioner System
Turbine Casing Flange Application with HRT
This tensioning device was designed for high ambient temperatures and minimum envelope restrictions, but is not limited to these capabilities. A tensioning method was needed that did not require special features on the stud for gripping. Using a threaded outside diameter of the nut as a gripping surface for tensioning satisfied this requirement. Studs can be accurately tensioned to the required load.
Hydraulic Rod Tensioner Features
- Varied materials can be utilized, especially those that are prone to galling due to torquing.
- Any number of Riverhawk Hydraulic Rod Tensioner tensioning devices can be linked together (daisy chained) to simultaneously provide a smooth uniform load on the flange connection.
- Fast and easy installation.
Difference Between Hydraulic Rod Tensioner and Legacy Style Tensioner
Riverhawk’s entire Hydraulic Rod Tensioner is not any larger than the nut itself. A legacy-style standard tensioner, commonly found in the industry, has a hex nut and exposed thread. The tensioning device has to fit over the nut, requiring a large footprint for the puller screw to grab onto the stud to apply tension. The Riverhawk Hydraulic Rod Tensioner fits within the same spot face and also does not require exposed thread. The tensioner was designed to use a special perforated nut that replaces the hex nut, allowing it to fit just over the outside of it. The whole diameter of the nut is no larger than the footprint of the hex nut.
Hydraulic Rod Tensioner Benefits
- High Load Capacity
- Minimum Footprint Required
- Easily Retrofittable
- Stud Extension Not Required
- Hydraulics Are Separate from Nut
- Large Range of Nut Materials Can Be Utilized
- Fully Simultaneous Tensioning Capability
- No Lubrication Is Required
- Controlled Coefficient of Friction
Riverhawk Hydraulic Rod Tensioner Components
- Tensioner – Simple hydraulic load cell
- Pin Platform – Goes through the nut and will be the acting force to stretch the stud
- Retaining Ring
- Hardened Steel Washer
- Cover – Aluminum, plastic, or low-grade steel
Riverhawk Hydraulic Rod Tensioner Process
- Take off the customer’s nut.
- Install the hardened steel washer to prevent pins pushing to dimple the flange face.
- Put on the perforated nut, with holes for the pin platform to go through (do not screw all the way down, back off ¼ of a turn so the washer does not have load applied, allowing a slice space between the flange face and the nut, eliminating the possibility of the nut getting seized on or stuck in place).
- Bring the lock ring down, take the spanner wrench and put it on, which gives it a snug, locked-in-place, movement-free fit.
- Push the pin platform through the nut by lining up the holes and pins, allowing it to fall into place.
- Thread the tensioner snuggly down to the locking ring.
- Hook up the hydraulic hose and apply the exact specified pressure, which is calculated to give the exact clamping force required for the joint to be tensioned.
- Increasing pressure will push the pins through the hydraulic nut, stretch the retaining ring, and lift off the flange face, tensioning the nut.
- Release the pressure, and remove the hydraulic nut and pin platform.
Click here to watch a demonstration of the Riverhawk Hydraulic Rod Tensioner in action!
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Tim Cain is a Sales Engineer at Riverhawk Company and has been with our organization since 2001. Tim holds a Bachelor’s of Applied Science in Electrical and Electronics Engineering degree from SUNY Polytechnic Institute.