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Hose Clamp Design/Engineering Assistance

  • Self-Compensating vs. Screw/Worm Hose Clamps

    Rotor Clamp Self-Compensating Hose Clamps

    Expands/contracts with the hose in response to temperature changes. Cannot be over/under tightened. Can be installed automatically eliminating Carpal Tunnel Syndrome (CTS), a nerve disorder of the hand and wrist. Less time for assembly – resulting in lowered production costs.

    Screw/Worm Type Hose Clamps

    Must be manually adjusted as temperature changes. Screw mechanism may be over/under tightened causing damage/leakage to the hose. Must be manually installed. More time needed for assembly/disassembly due to screw adjustment.

  • Joint Design

    Successful joint design is a step-by-step process that begins with your specific application requirements. Understanding your goals and knowing exactly what you want to accomplish with your system is an excellent first step. Your next best step involves three key joint design elements….hose, fitting and clamp…including performance data and critical specifications. This knowledge will help you make intelligent choices to better serve the application requirements of your design. Two important considerations in good joint design are sealability and hose assembly. Most obviously, the design must ensure that the hose does not leak fluid once installed on a fully operational system. Also, an operator working on a typical assembly line should be able to install the hose without expending too much effort.



  • Hoses

    Assembling a hose over a fitting involves a characteristic known as interference. This refers to the fit between the inside diameter (ID) of the hose and the outside diameter of the fitting. Interference is something you’re penalized for in football, but in the game of joint design, the more interference, the better the seal. There is an important relationship between interference and push on force. As the former increases, so does the latter. Although more interference is desirable, it must be balanced against the increased effort an operator would have to expend in order to install the hose on a fitting. In general, a line-to-line fit is a minimum requirement to ensure effective sealability. For example, a 2" hose ID and a 2" diameter fitting is a line-to-line fit. In general, any clearance fit between the ID of the hose and the diameter of the fitting is unacceptable since it can lead to a joint leak. A HOSE IS A HOSE… …Or is it really. The fact is, there are many types of hose constructions and materials. The one you ultimately decide upon will be the one that best suits your applications. There are many types of hose constructions and materials. A common automotive type is EPDM rubber compound with a Shore A hardness of 60 durometer. Other materials of construction are silicone or a combination of EPDM and silicone. Many are reinforced with an inner layer of woven fabric. Here are some general characteristics you should know about hoses:

    • A. The hose is named after its nominal, inside diameter. For example, a 1" hose is one with an inside diameter of 1".
    • B. The outside diameter depends on the wall thickness, which varies depending upon the hose type and construction. It is important to specify a hose with a closely controlled wall thickness, the smaller the tolerance the better. This will aid in sizing the clamp for the application.
    • C. Constant tension type clamps transmit force more easily through a hose with a thin cross section.
    • D. A higher hose durometer (hardness) means the hose is less compliant and more difficult to install. Lower durometer hoses allow the clamp to translate its force directly to the sealing surface of the fitting.
    • E. The straighter the angle of the hose, the easier it is to install.


    The Society for Automotive Engineers recognizes two basic types of hoses for heater and radiator applications. They are described below. (For a more detailed explanation of these and other hose types, see SAE specification J20). SAE 20R3—Heater Hose--Used for heater systems in ground and transportation vehicles. Wall thickness range: for sizes less then 25.4mm, the OD is the target ID +8mm (total wall), ±0.8mm. For 25.4mm size, the OD is 34mm ±1.2mm. SAE 20R4—Radiator Hose, Normal Service Type—Radiator hose for coolant circulating systems of automobile engines. Wall thickness range is 4.3 To 5.6mm for sizes smaller than 50.8mm and 4.3 to 6.4mm for sizes 50.8mm and larger.

  • Hose Clamps

    Rotor Clamp constant tension type hose clamps will compensate for changes in joint diameter due to compression set in a hose. This feature eliminates leaks and the need to re-torque a clamp. Factors to consider when sizing a clamp:

    • CTB type clamps: The clamps have a number designation equivalent to the outside diameter of the joint to be clamped, expressed in millimeters (Ex.-CTB-27).
    • HC (SAE Type "E"), HW and DW (SAE type CTW )- Clamps have a range of recommended application diameters, listed on the spec pages as "A, B and C" diameters. The nominal diameter of the clamp is the clamp size divided by 16.
    • The joint diameter will equal the fitting outside diameter plus twice the wall thickness, including the tolerances associated with each.
    • The clamp must be large enough to fit over the maximum diameter of the joint bead and hose at this point (see illustration).


    You can use a smaller clamp on an application to increase force. This can be done by placing the clamp on the fitting, installing the hose and sliding the clamp "backwards" up to the bead. Ideally, a clamp should be sized to fit onto the joint when opened to 90% of full (as a safety factor) and close to no less than the nominal (size) diameter when in the final position.

  • Fittings

    The fitting is the portion of the joint over which the hose is installed. To reap the full benefits of a constant tension clamp joint, the fitting should have the following characteristics:

    • The fitting should be round (within .003 inches).
    • There should be interference between the fitting and the hose, typically between 5% and 10% of the hose inner diameter. (Ex. A 1" nominal diameter hose could have a 1.062" diameter fitting for a 6.2% interference fit. All tolerances should be considered when calculating this diameter).
    • The surface of the fitting should be free of pits, scratches, "dents," parting line mismatches, and any surface defect that might cause a leak. The fitting should contain a bead that will prevent slippage under conditions of pressure where the hose is not constrained.
    • The bead diameter should be sized in such a way that the clamp can be installed over the assembled joint yet provide as much interference as possible and still facilitate acceptable assembly push on force.
    • The bead width and shape should be as small as possible and still allow for easy insertion of the hose onto the fitting.
    • The bead should be symmetric and should not compromise the geometry of the joint (roundness, surface defects, etc.).


    The fitting must be of the design diameter for a length of approximately 15/16" after the bead. That is, all dimensional constraints must be followed. This is necessary to seat the clamp. This means any bends, twists, diameter changes or the like can not occur until after the area in which the clamp will seat.

  • Materials & Finishes

    Rotor Clamp hose clamps are made from the following materials:

    • HC, HW Single wire clamps and DW double wire clamps-Specially processed premium grade spring wire, hardened and austempered to meet the performance requirements specified in the Rotor Clamp catalog.
    • CTB Constant Tension Band Hose Clamps-SAE 6150 Chrome vanadium (DIN 17222 and JIS G 4802) and SAE/1074.
    • CTL: SAE 1060-1090 Spring Steel, Austempered


    HC, HW Single wire clamps and DW double wire clamps— Peen-plate zinc (non-electrolytic process) .0002" minimum thickness plus dichromate treatment. Offers 48 hours of salt spray corrosion protection.
    CTB Constant Tension Band Hose Clamps - Magni 511 finish offering 480 hours salt spray protection per ASTM B117. It is a chrome-free duplex coating system that combines an inorganic zinc-righ basecoat with an organic topcoat. It meets the following automotive specifications: General Motors: GM-7111-M; GM-7112-M; Ford Motor Company: ESA-M21P5A; Ford World Wide: WSD-21P11-B1; WSD-21P11-B2; Chrysler Corporation: PS-7626.
    CTL Constant Tension Light Band Clamps - Phosphate: mechanical zinc plate.

  • Assembly Considerations

    Clamps should be installed with specific pliers recommended for the type of clamp being used. Expansion of the clamp beyond the intended operating diameter will diminish the force that the clamp can apply. Any lubricating substance used to aid assembly of the hose must never be in contact with the clamp. (See Lubricants section).

  • Lubricants

    Many use some type of lubricant to ease the installation of a hose onto a mandrel or fitting. But some types of lubricants can be harmful to a clamp that is installed on the hose. Here are a few guidelines to help minimize clamp failure: Clamps are not recommended to be put in contact with water based hose lubricants. Any lubricant which is water based has the potential of causing stress corrosion cracking. Water alone can cause the failure. Oil based products are the only products that Rotor Clamp can recommend. The type of lubricant used depends on compatability with the hose type. Hose lubricants should be applied to the I.D of the hose only. There is no need fro the O.D. of the hose to contain a lubricant. (It should be noted that any product that helps installation on a hose may also allow it to slip off easily.) Examples of lubricants known to cause clamp failure include acetone, chlorine, flourine, mineral oil, dish detergents and laundry detergents. Rotor Clamp tests each hose clamp lot for stress corrosion cracking by induced hydrogen embrittlement. This test is performed on expanded clamps, and after the alloted time, parts are rinsed to test susceptiblity to breakage. If parts break, they are oiled. Oiled parts are retested, and have passed 100% of the time. Rotor Clamp can provide oiled clamps for customers. (Clamps with dorrlflake are not susceptible to this condition.) If you have any questions, please contact Rotor Clamp at 1-800-547-6867, or contact us.


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