A Beginners’ Guide to Torque Wrenches

There are two main types of hydraulic torque wrench, the Square Drive wrench and the Limited Clearance wrench (also known variously as Low Clearance/ Direct Fit/ Cassette/ Hex Link wrench). The Square Drive wrench drives a socket whereas the Limited Clearance wrench fits directly on the nut. The vast majority of hydraulic torque wrench tool systems are "double-acting" (hydraulic advance, hydraulic return back over the ratchet) although single-acting (hydraulic advance, spring return back over the ratchet) systems are available and whilst few manufacturers/suppliers cater for this option, the single-acting system can bring advantage in terms of cost and on remote, difficult-to-access bolting applications where a power source is not readily available.

The Square Drive wrench is by far the more versatile of the two wrench options in that it will drive any AF size socket with a suitable drive. The Limited Clearance wrench requires a bespoke AF size hex link for each size nut which can make it expensive to assemble a suitable range of equipment for all bolt sizes. With good operating habits, both wrench types are easy and safe to use although the Limited Clearance wrenches are generally more suited to flange work than their Square Drive counterparts.  Given a choice on any bolting job where either wrench type can legitimately be used, I would personally opt for the Limited Clearance wrench as it negates much of the twisting force and reaction challenges often experienced by the Square Drive wrench. Having said that, the Square Drive wrenches find more favour with our customers which is indicative of their much greater versatility and resultant cost effectiveness.   

The wrenches are powered by a hydraulic pump. Most Torque Wrenches systems nowadays are designed to work to a maximum pressure of 10,000 psi (710 bar). The pump pressure, as measured by the pump pressure gauge and locked in at the desired rating, dictates the torque output of the wrench. Typically, the pumps are either air or electric powered (usually 110V) although the single-acting wrenches can be powered by any 10,000 psi pump including manual hand pumps.  The wrenches are connected to the pump by a high pressure siamese hose (or single hose for single-acting wrenches) usually around 5m in length although can be any length within reason.

The most commonly used wrenches tend to be 3/4" and 1" Square Drive Wrenches with maximum torque outputs ranging from 1000Nm up to 4,000 Nm and their Limited Clearance counterparts - accommodating nut AF sizes up to 80mm - up to around 5,000 Nm. Beyond these, the Square Drive wrenches ( 1 1/2" and 2 1/2" drives) and Limited Clearance wrenches in most tool ranges accommodate tightening torques up to and in excess of 30,000 Nm for working on large bolts. 

Gulf Incon, an authorized dealer of SPX Bolting system in UAE offers hydraulic torque and tensioning systems, industry specific certified training programs, system rentals, and flange management database software etc. If you need more about torque wrenches or bolt tensioners  feel free to contact us and our experts will guide you.