Hydraulic Bolt Tensioner : When Accuracy Is Not An Option

Before we get into when to use a hydraulic bolt tensioner for bolting — let us explore what a bolt tensioners is, what is does, and what challenges it solves.

What is bolt tensioning?

From an engineering prespective, tensioning is the direct axial stretching of the bolt to achieve preload.

In laymen terms, bolt tensioning is the stretching of a bolts stud [ the female threaded part] until the nut is optimally secured.

This approach actually preloads the bolt, stretching it before you completely install the nut.

The Hydraulic Bolt Tensioner

There are several tools you can use to tighten and loosen a fastener. Only one of them will stretching the bolt’s stud. You guessed it — the hydraulic bolt tensioner.

The stud tensioner as it is sometimes called, as well, is powered into action by hydraulic oil as you will soon see. But, first …

Preparing your hydraulic bolt tensioner before adding hydraulic pressure

Before, the hydraulic nut is fastened, there are some safety and mechanical steps to follow.

Today, we be using the Riverhawk Hydraulic External Tensioner, as called HET bolt tensioner, to demonstrate the pre-bolt tensioning steps needed to properly and safely bring a flange joint together.

NOTE: All bolt tensioner manufacturers have slightly different bolt tensioning preparatory guidelines, so always read the safety and instruction manual accompanying your hydraulic bolt tensioner.

Tweet: Manufacturer's rating of pressure & load are maximum safe limits. Best practice encourages using only 80% of these ratings! #AMGBoltingTipsManufacturer’s rating of pressure and load are maximum safe limits. Good practice encourages using only 80% of these ratings!

4 Steps to take before seeing your hydraulic stud tensioner in action.

Riverhawk HET bolt tensioner comes with a special nut ring
Image Credit: Riverhawk
Step #1: Place special nut ring over the nut



Step #1: The Riverhawk Hydraulic bolt tensioner comes with a special nut ring, which is to be place over the hex nut.

It rest on the top flange. Notice there exists a gap between the joint flanges.


Buy the Riverhawk HET hydraulic bolt tensioner from AMG Bolting Solutions
Image Credit: Riverhawk
Step #2 – The bolt tensioner less the puller is placed over fitting.





Step #2: Once the special nut ring is set in place, the hydraulic bolt tensioner — minus the stud puller — is placed over the stud, hex nut, and special nut ring until the bolt tensioner is resting on the flange.




Step #3 –  Once you have your Riverhawk HET in place, you may then insert the stud puller. As it’s name applies this is the part of the hydraulic bolt tensioner that will stretch the bolt’s stud.

As depicted in the three images that follow the stud puller should go into the HET smoothly. Once you feel it touching the stud you are ready for the next step.

Hydraulic Bolt Tensioners for sale
Image Credit: Riverhawk
Step #3a – The stud puller is inserted.
What is a hydraulic bolt tension
Image Credit: Riverhawk
Step #3b – The stud puller should insert smoothly
Where to buy a hydraulic bolt tensioner
Image Credit: Riverhawk
Step #3c – Insert the nut puller until it touches the top of the stud.











Step #4 – Next, use your hand to manually screw the stud puller into the female threads of the stud itself.

WARNING: If you use a bolting tool to tighten the stud puller you could tighten it too much cause a bolt failure.

You want to make certain you screw the stud puller until it is touching the hex nut completely.

Best hydraulic power pump for bolt tensioning
The Highflow 115/230 V Power Pack


Once, the puller is in place you are now ready to add your Enerpac hydraulic hose and your Torc hydraulic power pump pack unit.

[Side note: AMG Bolting Solutions offers 6 different hydraulic power pump packs for bolt tensioning.]

Make certain the hydraulic hose is securely fastened on both the bolt tensioner compression fitting and your pump pack compression fitting.


hydraulic bolt tensioner use a stud puller to stretch the female threaded stud
Image Credit: Riverhawk
Step #4a – Screw the puller over the stud until the puller touches the nut ring
Buy a hydraulic hose and find hydraulic pump packs for bolt tensioners on sale
Image Credit: Riverhawk
Step #4b – Attach your hydraulic hose and power pump pack












Finally, you can turn your hydraulic pump pack to see…

How a hydraulic bolt tensioner works

HYTORC hydraulic pumps for Enerpac bolt tensioner on sale
Image Credit: Riverhawk
Pressure is begin applied to the stud.



When hydraulic pressure is added the stud is stretched.

This separates the hex nut from the joint flange, which makes it easier and quicker to run the nut down to the base of the joint flange.

Run down your nuts faster with a bolt tensioner
Image Credit: Riverhawk
Tommy Bar being used to turn nut.



With pressure still applied, the nut is run down with a bolting tool call a “Tommy Bar”.

[ Sorry Chris Farley fans — not what you are thinking, but yes, funny.]

The Tommy Bar is inserted into the special nut ring, and manually turned.

Releasing pressure from your bolt tensioner
Image Credit: Riverhawk
The spring pushes into place.





Next, you release the pressure by turning off the hydraulic power pack.

Upon releasing the pressure from your bolt tensioner the built-in spring will push the cylinder back down into place.





That’s it. The load on the stud has been released. Now, simply unscrew the stud puller with ease.

Disconnect the hydraulic hose, and lift up the bolt tensioner.

Hydraulic Bolt Tension and Power Power Systems for sale
Image Credit:
RiverHawkPuller and hose removed
Hydraulic Nuts for sale
Image Credit: Riverhawk
HET bolt tensioner removed.


Your the nut is snug against the flange, pressure in the load cell is released, and a clamping force has now been transferred to the bolted joint.

Basically, what has happened is the stud remains stretched and the load is locked in, and you are ready to tighten the next nut in accordance with your bolt tightening sequence / pattern.





Now, that you know what stud tensioning is and how a hydraulic bolt tensioner works. You are ready to learn when the choose a bolt tensioner over a hydraulic torque wrench, or a pneumatic impact wrench.

The key to knowing if a bolt tensioner is needed is to understand its benefits fully.

7 basic reasons to use a tensioned product versus a hydraulic torque wrench

Whenever you need to achieve the most consistent amount of bolt stretch and clamping force bolt tensioning is your only option.

Let’s be clear about something. We love how a TORC hydraulic torque wrench performs. That is why we sell them.

However, we are not so naive to believe that every situation requiring a nut and bolt is best answered by using a square drive tools or limited clearance tools.

Plant Managers and Maintenance Supervisors – perhaps like you — are consistently looking for ways to run their facility more efficiently, and cost effectively.

When leaks from bolted flange joints occur you ask — “could this have been prevented?” Typically, the answer to the question is a resounding — “YES!”

As it turns out, leaks of this nature are indeed an unnecessary economic and environmental cost to your facility.


Hydratight, owned by Actuant — the same company that owns Enerpac —  is manufacturer of hydraulic bolting equipment.

On their website, they make a great case for bolted joint flange integrity stating,

Nearly all of the world’s process plants and components are either welded or bolted together. A welded joint has mandated procedures and competency requirements to assure its quality and fitness for purpose. Yet the bolted flange joint historically has few such requirements, despite serving the same purpose – pressurized process containment.

In conjunction with this statement, they offer an illustration [Figure 1: Welded Joint versus Bolted Joint] to explain what needs to happen to ensure bolted flange joints do not leak.

Welded Joint versus Bolting Joint - AMG Bolting Solutions love TORC hydraulic torque wrenches, but sometimes a bolt tensioner is the best solution. Avoiding leaks on bolted flange joints by applying bolting standards similar to welding standards.
Figure 1: Welded Joint versus Bolted Joint – 
Avoiding leaks on bolted flange joints by applying bolting standards similar to welding standards.

This recommended procedure works with lot types of bolting solutions. However, there are some red-flag points, which should lead you toward using a hydraulic stud tensioner.

Material Control :

  • Are the bolt and nuts standard, or custom?

Standard = Torquing and/or tensioning is fine.

Custom = Tensioning would be best.

  • Would the margins from the task cover the cost of equipment repair service — if needed.

No = Manually, torquing  is your best option. Be careful — busted knuckles hurt really bad.

Yes = Use either a hydraulic torque wrench, or a bolt tensioner.

Competent Personnel :

  • Does the job you are completing satisfy the need for a trained hydraulic bolting tool specialist.

No = Manually, torquing  is your best option. Here we go again, watch out for — busted knuckles — ouch!

Yes = Use either a hydraulic torque wrench or a bolt tensioner.

  • Zero bolted joint leaks is always the goal, but, so is zero workplace accidents. Nice, goal, but, sometimes these things happen. The question, if/when a leak occurs will the deadly and/or will impact to environment, be potential  harmful, but not deadly, or only cause some downtime.

Only cause some downtime = Manually, torquing  is your best option. Please wear gloves.

Potentially harmful to humans, but not deadly = Use either a hydraulic torque wrench or a bolt tensioner. Also, we recommend you move joint flange inspection to your daily TPM checklist, if you have not done so already.

Deadly, will impact the environment = Do not take a chance here. The risk is too large. Ask BP, they will give you 18.7 billion reasons, beyond harming wildlife why you do not want to go cheap here.

Use a bolt tensioner or a hydraulic nut.


Snapshot of Bolt Tensioner Benefits:

A hydraulic tool that is safe, reliable and delivers repeatable results.

Clearly, the use of hydraulic stud tensioners have some advantages over other tightening methods depending on need, application purposes, risk management, and cost of operation:

Direct: Tension is applied directly to stretch the bolt stud, therefore you don’t need to strain against friction manual wrenches, or experience load losses when using a hydraulic torque wrench.

Accurate: The applied load is controlled in an extremely accurate manner, because the load is directly proportional to the pressure applied to the bolt tensioner by the hydraulic pump.

Calculated: The load transfer factor is most acutely calculable. This helps to give maintenance personnel the correct residual load.

Fast: Operation of tensioned products improves accuracy, which in turn reduces time required to re-tighten the load.

For example, the Enerpac GT4 hydraulic tensioner turned a 10 hours job of removing studs into a roughly 30 minutes operation. Read official case study >>>

Versatile: Tensioning permits the simultaneous tightening of multiple bolts; the tools are connected in sequence via a high-pressure hose assembly to a single pump unit.
Reliable: Uniform bolt loading ensures each tool develops the exact same load and provides a uniform clamping force across the joint.
Stress-free: Purely axial, tensile loading ensures no torsional stresses are introduced.

Selecting the right bolt tensiner

The proper bolt tensioner needs to be selected for each application, which requires gathering important data, such as:

  • Nut size
  • Bolt diameter
  • Washer thickness and diameter
  • Protrusion length of free stud
  • Bolt load requirement
  • Bolt grade


Key Takeaways:

  • Hydraulic bolt tensioners are the best method of tightening a flanged connection.
  • Most commonly, these multiple linked stud tensioners operate together to stretch their respective studs.
  • The nuts are lifted from the flange, then run down to seated position.
  • The hydraulic pressure applied to the bolt tensioner controls the amount of bolt stretch.
  • When the bolt is pre-stretched by the tensioner, only minimal torque is needed to tighten the nut.
  • As the tensioner is released, the natural elasticity of the bolt provides the proper clamping pressure.
  • AMG Bolting Solutions offers several elite brands of bolting equipment you need to successful fasten even the rough nuts with a hydraulic bolt tensioner.


A comprehensive guide to selecting the proper power pump for your bolting projects. If you would like to be notified every it is released, email us at: AMGpumps@dirinc.us,  or call 574-329-9022.