Piping Technology & Products' constant spring hanger, usually referred to as a constant, provides constant support force for pipes and equipment subjected to vertical movement due to thermal expansion at locations where maintaining a constant stress is critical. This constant resistance is achieved by having two moment arms pivoted about a common point. The load is suspended from one of these arms, and a spring is attached to the other. With an appropriate choice of moment arms and spring properties, a resisting force can be provided that is nearly independent of position.As with variable springs, Type refers to the connection of the constant to the structure and the pipe. Figure 4 shows the attachment for Types A – E. The designation Figure 100 and 200 refer to the orientation of the spring can. This is vertical for Figure 100, and horizontal for Figure 200.
Travel stops are installed in all constants before shipping. These must be present during any hydro testing, but must be removed during installation before normal operations. They are usually pins, but in some cases may be keys. See note below on travel key removal. In either case, the load must be adjusted so that the travel stop is easily removed. |
Caution: Do not force the travel stops.
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| Figure 4: Constant Hangers Types A – E. |
Types A – E Constants (100 & 200)  Back to Top
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| Figure 5: Travel stop position. |
- Secure the hanger to a structure capable of handling the operating load, at a point where the constant's load coupling is directly over the desired point of attachment to the pipe in the operating position.
- The moving parts of the constant should be unobstructed and free to move.
- Attach the connecting rod to the load coupling with full thread engagement.
- Transfer the load by turning on the load coupling before removing the travel stop.
- If required, hydro testing should be done at this time.
- Once the load is transferred, the travel stop must be removed. The travel stop (painted red) should now slip out easily. If not, refer to Figure 5. The travel stop pin must be moved to the center of its hole by adjusting the hanger load. The hanger load needs to be increased if the pin is in position A, or decreased if the pin is in position C. Once disengaged, the travel stop may be stored by hanging it from the constant.
- The hanger load should now be readjusted to the cold position.
- When the operating conditions are reached, check the hanger to assure the indicator is at the hot position. If necessary, adjustment should be made by turning the load coupling to align the indicator to the hot position.
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Type F - 100 Constants Back to Top
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| Figure 6: F - 200 Type constant, and Travel Stop Pin positions. |
- Secure base plate to the structure.
- If the constant is of the platform type (see Fig. 6), place the pipe on the platform, and attach it to the platform. If there is no platform, attach a strut to the piping, then to the constant support.
- Hydro test line if necessary.
- The travel stop should be in the middle of its hole. If the travel stop is in the A- configuration (see Fig. 5), contract the strut, and if it is in the C- configuration, expand the strut to force the travel stop pin to move to the center of the travel stop hole. When the travel stop pin is centered in the travel stop holes, it can be easily removed and the constant is ready for operation.
Danger!! If pin can not be easily removed after struts adjustment, do not drive pin out. |
Type 200 - F Back to Top
The Type 200 - F constants are shipped with an Installation Rod and a Travel Stop Pin.
- Attach the base plate of the constant to the supporting structure.
- Attach the constant's support platform to the pipe using a pipe shoe or other suitable support. If the clearance is tight, temporarily force the table down by tightening the installation bolt (see Fig. 7).
- Loosen the installation bolt or bolts to allow the load flange to rise up to the installed height. If the clearance is loose, shim or grout the constant or pipe attachment accordingly.
- Hydro test line if necessary.
- If travel stop is in the A-configuration as shown in Fig. 5, extend the installation bolt (or bolts) to force the load flange up so that the pin is in the center of its hole. If the pin is in the B configuration, contract the installation bolts. When the travel stop pin is in the center of the travel stop hole, it can be easily removed.
- Loosen and remove the installation bolt for the 200-F. The constant effort support is now ready for operation.
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| Figure 7: Type 200 - F |
Type 200 - U (Upthrust) Constants Back to Top
| The installation of the Type 200 - F and Type 200 - U constants is the same, except that the Type 200 - F has one installation bolt, and the Type 200 - U has four. |
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| Figure 8: F-200 Type Constant, and Travel Stop Location |
- Attach the base plate of the constant to the supporting structure.
- Attach the constant's support platform to the pipe using a pipe shoe or other suitable support. If the clearance is tight, temporarily force the table down by tightening the installation bolts (see Fig. 8).
- Loosen the installation bolts to allow the load flange to rise up to the installed height. If the clearance is loose, shim or grout the constant or pipe attachment accordingly.
- Hydro test line if necessary.
- Loosen the nuts to allow maximum movement. The constant effort support is now ready for operation.
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Type G Constant Back to Top
The Type G constant consists of two Type 100 constants connected by a beam, with the pipe being supported on the beam.
- Support the pipe at the desired elevation.
- Attach load rods to the structural support.
- Attach the constant to the load rods using the turnbuckles provided.
- Using the turnbuckles, level the pair of channels connecting the two constants.
- Keeping the channels level, transfer the pipe load to the constant, either by raising the constants or removing any temporary support for the pipe.
- If hydro testing is required, this should be done now.
- Remove the travel stops. If they are not in the center of their holes, use the turnbuckles to adjust the load so that the stops are in the center. They should be easily removed. If not, adjust the load until they are.
Do not drive them out.
- Using the turnbuckles, adjust the load indicator to the cold position.
- After the load reaches normal operating conditions, check to see that the load indicator is at the hot position. If not, adjust with the turnbuckles.
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| Figure 9: G Type Constant |
Field Instructions for Load Adjustment, Fig. 100 & 200 Back to Top
Under no circumstances should an attempt be made to remove the lock nut and the load adjustment nut from the constant spring hanger.
Every constant spring hanger is calibrated in the factory and set to the load specified on the nameplate. Load adjustment in the field is discouraged as it may significantly change the system.
However, to provide for situations where the supported load is different from the calculated load, the constant spring hangers are equipped with load adjustment capability. The load adjustment capability consists of a load adjustment scale and indicator, which are used to increase (Figure 10A) or decrease (Figure 10C), the load by 10%. Thus, a 2000-pound hanger can be adjusted for loads from 1800 to 2200 pounds. The travel stop pin must be engaged before load adjustment is performed. Adjusting the load to higher or lower load from the load specified on the nameplate using load adjustment is approximate and not recommended. |
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| To increase the cold setting be sure that the travel stop pin is in place. Then loosen the lock nut at the end of the spring. Tighten the main nut, then retighten the lock nut. |
| To decrease the cold setting be sure that the travel stoop pin is in place. Then loosen the lock nut at the end of the spring. Loosen the main nut, then retighten the lock nut. |
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| Figure 10: Field adjustment for load. The Load Adjustment Scale is located on the spring can, near the adjustment nut. |
Constant Hangers with Adjustable Travel Stop Keys: Removal of Travel Stop Key Back to Top
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| Figure 11: Adjustable Travel Stop Keys |
- After hanger installation, remove the travel stop hex nuts from both sides. Check whether A-face or B-face of the threaded bolt is in constant with the travel stop keyhole as illustrated in Fig 11, above.
- If the B-face of threaded bolt is in contact with the travel stop keyhole as shown in Figure 11, turn the turnbuckle clockwise. The travel stop bolt will move towards the center. At this point, the load has been transferred and the constant hanger is balanced with the pipe weight. The travel stop key can be easily removed.
- If the A-face of threaded bolt is in contact with the travel stop keyhole as shown in Figure 11, turn the turnbuckle counterclockwise. The travel stop bolt will move towards the center. At this point, the load has been transferred and the constant hanger is balanced with the pipe weight. The travel stop key can be easily removed.
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