Damper Specifications

General

  1. The damper shall be supplied by an established manufacturer who’s principle product is industrial dampers and has a minimum of 20 years experience in the design and application of industrial dampers. The dampers must be offered with a guarantee of workmanship and performance.
  2. All welding and fabrication shall be to high quality industrial standards. Tolerances to be held to industry accepted steel fabricating tolerances to insure proper fit and operation.
  3. The damper shall be hand cleaned to remove weld spatter, burrs and loose mill scale. Carbon steel surfaces to be painted one shop coat of rust inhibitive industrial primer.
  4. The damper shall be shop tested for proper mechanical operation a minimum of 10 times from full open to Full closed position before shipment.

Structural 

  1. The damper shall be fabricated from new materials and designed to be self supporting. Proper selection of materials and cold clearance allowances shall be made to insure proper operation at the design conditions. 
  2. There shall be a minimum of 1/8″ corrosion allowance on all interior components exposed to the air stream in corrosive applications.
  3. The damper shall be suitable for the system design conditions as stated in the Damper Specification Data sheet.
  4. The damper is to be designed for proper operation in the specified installed position.

Construction

  1. Frame: Welded frame with bolting Flanges. Frame to be structural, formed or welded of sufficient size and strength to be self supporting and to prevent permanent “racking” prior to installation. 
  2. Vane(s): Multi-vane dampers to have double thick airfoil vanes welded to the shaft. Single vane dampers to have a two piece vane, formed to wrap around and be welded to the shaft. Vane stiffeners are to be provided when damper size or operating conditions dictate. 
  3. Shaft(s): Shaft(s) shall be one (1) piece continuous through shafts. 
  4. Packing Glands: The packing glands shall be adjustable and the packing must be replaceable without the removal of the bearing. 
  5. Bearings: The bearings are to be self-aligning of a suitable type to assure proper operation at the maximum operating temperature. The bearings are to be mounted outboard on standoffs over the adjustable packing glands.
  6. Vane Seals: The vane seals are to be bolted for ease of replacement unless they are the metal bar seat or scissor seat in which case they may be welded.
  7. Linkage: Multi-vane fixed linkages are to be outboard with bronze bushings at all pivot points. An adjustable linkage shall be utilized on tight shutoff dampers in high temperature applications to allow for field adjustment at operating temperature conditions. All levers shall be pinned or keyed to the shaft. Welding of levers to the shaft is not permitted. 
  8. Operator: The operator shall be shop mounted, calibrated and tested prior to shipment. Power operators are to be sized at a minimum of 1. 5 times the calculated torque for safety factor. The operator mounting bracket and coupling are to be sized with consideration of the operator torque to prevent twisting and distortion of the bracket and the damper frame at the maximum torque condition. 

Approved Supplier

Multi-vane Dampers: Kelair Products, Inc., Model LSI

Butterfly Dampers: Kelair Products, Inc., Model BRI (round), Model BRI-M (round), Model BSI (rectangular or square)

Damper Design Considerations: 

This is a list of potential reasons for field problems and damper failure if proper consideration is not given at the specification and design stage. This accumulation of information is the result of years of damper design and application experience and is intended as a guide for the Design Engineer to assist our customer in specifying and purchasing quality dampers that will meet the needs of their application.

  1. Standard damper blade rotation is CCW as viewed from the operator side of the damper. Specify blade rotation if it is critical to proper air flow. For example, if a blade rotates next to an elbow, the blade rotation should be such that the blade acts as a turning vane. Improper rotation in this instance can cause severe turbulence.
  2. Consideration must be given to damper blades that will protrude outside the damper frame when in the full open position which may strike adjoining transitions, expansion joints, turning vanes, etc. It may be necessary to specify that the damper blades must not extend beyond the damper frame.
  3. Make sure to specify if the damper will be required to seal against or be subject to a reverse flow condition. Some dampers are designed to seal against a flow in one direction only.
  4. An access door in the duct near the damper is recommended for damper servicing if the damper cannot be easily removed.
  5. Advise the damper manufacturer if the damper will be subject to abrasive, corrosive or heavy sticky deposits that can build up on or corrode damper blades and seals. Any expected accumulations in the bottom of the duct that may interfere with blade movement or sealing must also be advised. Standard damper design is for shafts to operate in a horizontal position. Advise the damper manufacturer if the damper is to be installed in any position other than horizontal. This is especially important For dampers that are operated by a chain wheel or counterweight.
  6. Specify the mounting position for guillotine and slide gate type dampers. Example: Vertical top entry, vertical bottom entry, horizontal on edge, horizontal flat.
  7. Provide structural support or an expansion joint at the adjoining duct to prevent stressing of the damper frame. Compressing or twisting the damper frame can cause seal failure and/or blade jamming.
  8. Specify “Right Hand” or “Left Hand” damper construction for proper operator position and blade rotation when dampers are to be used in pairs such as dual blower outlets.
  9. Insure that the damper operator and drive linkage are sized with sufficient safety factor to allow for operation of dampers that become corroded, deposit or thermal bound. Undersized drives are a major cause of damper failure.
  10. The opposed linkage should be avoided on dampers when tight sealing is required. The opposed action of the blades make tight sealing difficult. The opposed linkage should be used for throttling or modulation control. The parallel linkage should be used for on/off and tight shutoff applications.
  11. Consider a corrosion allowance on internal components. A 1/8″ corrosion allowance is normal in a high corrosion application. Sometimes stainless steel shafts and/or blades can be used at a nominal expense considering the extended service life of the damper.
  12. Stainless steel fasteners for seals, bearings and operating accessories can greatly reduce service cost and effort.
  13. When considering a damper fail position when using pneumatic operators, specify fail position on loss of air supply, electric supply or both. Fail open or close on loss of electric supply can be easily obtained by using a single coil solenoid valve and piping it so that it will power the damper to the fail position when the solenoid coil is de-energized. Fail open or closed on loss of supply pressure requires an auxiliary power source such as a spring, air reservoir or counterweight.
  14. When using a positioning device, specify open/closed position in relation to the positioning signal. Example: 4-20 MA or 3-15 PSI signal . Is the low signal to OPEN the damper with an increase in the signal to CLOSE the damper or visa-versa? Most positioners will fail to the low signal position on loss of input signal, however, there are positioners available to fail in place on loss of input signal if this is required.

This is only a partial list of helpful hints. At Kelair Products, Inc., we evaluate all applications for proper design to insure proper performance. Complete operating conditions are vital to making a proper evaluation. we will be glad to discuss your particular application or problems with you.

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