Ruland Uni joints – 2 reasons to buy Twin Spring

Mechanical power transmission couplings alternative

Ruland Uni joints

Uni joints like all universal joint manufacturers all revolve around the same design, Ruland is no different so all u joints are the same, some of the internal components are different, the hubs can be made stronger but that also increases the price. The universal joint is all the same whether a friction bearing block and pin or a needle bearing type.

The couplings are the same and have the same issues of maintenance and a lack of flexibility. This lack of flexibility added to the maintenance required to make the coupling continue to function due to the build up of heat and the grease or lubrication that is required to keep the uni joints functioning.

Ruland uni joints design while similar to all other Uni joints is broken into two different offerings, these couplings or universal joint regardless of type still are a 3 part design so contains bearing cross and two hubs or yokes.

Their model range is split into two UJ-HD and UJ-HS. UJ-HD875 is their small u-joint, the UJ-HD1000 and UJ-HD1125 is their middle range and UJ-HD1250 and UJ-HD1500 is another middle of the road coupling, the models go up from there UJ-HD2000 and the range tops out at UJ-HD4000.

These UJ-HD models are all based off the friction bearing technology, so low speed, low to medium strength. The other range they offer is the needle bearing based u-joints, which include UJ-HS750, the UJ-HS875, the UJ-HS1000 and the UJ-HS1125.

The two ranges (the needle bearing model is the same technology as that of the Hardy Spicer Uni joint), they have two variations of the needle bearing coupling as well, the standard version or the premium which basically is a updated pre-greased bearing for longer life.

This comes at a increase in price and while this will increase the useful life of the bearing cross it too will need to be replaced as either the lubrication runs out or the bearings themselves just wear out and need replacement due to equipment failure or bearing failure

Friction bearing universal joint

Friction bearing uni joints is a simple design, a center block with 4 holes through it which holds 2 pins thus a friction insert which is the same as a block and pin universal joint.

Friction bearing Advantages – This universal joint design allows for high strength but low speed, so its a great low cost option to allow some industries that only need a low speed low misalignment shaft coupling but needs that high strength. Their application is usually not placing a high demand on the uni joints, as the couplings are not needed to be used in 24/7 setting

Friction bearing Disadvantages – It as a coupling can only run at low speed due to the design is such that it can only run at low speed because at higher speed the block starts to heat up leading to failure due to pin binding (generated heat makes the 2 pins expand leading to making the block seizing in the middle of the coupling)

Due to the single block in the center of the coupling, its ability to be used in a large misalignment angle is normally ruled out as there is nothing to absorb the vibration that results in damage to components and leads to increased  and that is the other reason it has to be used at low speed.

The universal joint design regardless of manufacturer has two hubs, a input hub and a output hub, these are used to connect from the input (motor or power source) to the output (usual a shaft or wheel etc.)

What models are available

Twin Spring Couplings current offerings compare to the following Ruland friction bearing U joint

Ruland USSK24, USSK20, UJ-HD875 and UJ-HD750 are comparable to our TSC150

Ruland USSK28 US32, USKK32, UJ-HD1000 and UJ-HD1125 are comparable to our TSC300

Ruland USSK40, US 40, UJ-HD1250 are comparable to our TSC500

Needle bearing universal joint

Needle bearing uni joints are more closely related to the Lovejoy u joints, and it also means increases, both in simplicity (pin and block with 2 pins to 4 bearings 4 snap rings, a zerk nipple and the housing to hold the bearings and feed the grease from the house to the bearings) and operating speed (6000 RPM compared to 1750RPM)

Needle bearing Advantages –  The advantages are two fold, an increase in angle of misalignment and an increase in speed of operation. The needle bearings means the angle of misalignment can increase to a maximum of 45 degrees (but only at low speeds and low load)  with less heat and more importantly no real increase in vibration.

The speed increases from only 1750RPM with the friction bearing to 6000RPM with the needle bearings. This is due to the fact that the needle bearings are constantly greased which reduces friction and thus reduces the heat generated at the higher speeds. The grease is either from the bearings shaft cross or the long life pre-lubricated bearings.

The other advantage of using the needle bearings is that the joint itself is able to be used at a higher angle of misalignment due to the bearings allowing a great range of misalignment verses the friction bearing design. This means both higher speed and larger angle of misalignment which makes it useable in far more industries and different applications.

Needle Bearing Disadvantages – The disadvantages are also two fold with the improved performance also means increased maintenance and increased replacement of wear parts, being the bearings. With the bearings now included inside the coupling the increased speed increases the friction so the bearings need to be constantly filled with grease to stop the needles in the bearing from expanding with the heat and seizing inside the race, the grease absorbs the heat rather than the needles bearings.

This means that the grease will dry with use and will constantly need to be replaced, this increases the overall cost of the coupling as the increase in maintenance costs lowers the ROI of the couplings. Now the other option is going for the more expensive bearings which adds to the cost of the u joint but means less lubrication intervals.

Another disadvantage with the inclusion of the bearings is, while they improve the flexibility of the coupling they also wear out as the bearings are used outside their typical usage, so the bigger the angle of misalignment they are used at, the increased rate of wear the bearings encounter since the needles are being forced against the side of the bearing cage.

This force wears the needle ends and bearing cage so the more force applied (ie bigger misalignment angle) means the needle bearings wear quickly and the bearing needs to be released sooner.

The other disadvantage of both universal joints is the hubs, the input and output hubs, the other design flaw is the “ears” of the universal joints that receive the bearings. Being machined down to a degree to accept the small bearings and angled to allow maximum angle of usage it also is an area where as a weak point they can crack or break under high stress or constant cycling on and off as in industrial motors.

Twin Spring Couplings current offerings compare to their needle bearing joints

Ruland USC20, UJ-HS750 are comparable to our TSC150

Ruland USKC24, UJ-HS875 are comparable to our TSC300

Ruland USKC32, UJ-HS1000 & UJ-HS1125 are comparable to our TSC500


How does Twin Spring Coupling differ from Ruland’s coupling


The Twin Spring Coupling has a number of advantages over the typical universal joint

No bearings so no greasing or replacing worn bearings

Twin torsion spring design means increased flexibility with increased torque

No central bearings or block , one central ball acts as the pivot point for the coupling, one ball means annual greasing, reducing maintenance costs

One piece design means input and output hubs are integrated into the coupling making it a one piece design verses a three piece design with a universal joint.

Spring design allow absorption of vibration and shock into coils reducing the likelihood of damage to sensitive equipment

The combination of the twin spring design means the same amount of flexibility as a universal joint but without the friction or needle bearings means it produced less heat but can still be ran at both low and high speeds means the best of both universal joint designs but without the downsides of either.

OK so we have one disadvantage, the Twin Spring Coupling is longer than a standard uni joint, why is that? As to make the coupling as flexible as their uni joints we have made it longer.

Available in all the same bore sizes, keyway sizes as well as the most common shaft sizes means it is a simple replacement for either of these two universal joints with the only difference being is the Twin Spring Coupling is slightly longer, this is because of the increased flexibility and the thickness of the torsion spring coils to account for the torque requirements of the machinery.

Time to improve on a 350 year design

Twin Spring Coupling when 1 is better than 3


For more information on our couplings go to

Industrial Coupling

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