IMPROVED STUFFING BOX DESIGN

IMPROVED STUFFING BOX DESIGN

In a conventional stuffing box design when the gland bolt is tightened, the packing is not tightened as a concentric force and, a portion of the force is diverted at a right angle to the stem. The actual tightening force is reduced "Distribution of Clamping force.) The result is the sealing pressure is effective in only the first 2 or 3 rings where the clamping force is suffcient. However, even those upper rings, if the sealant of binder etc. disappears, will cause leakage. It is difficult under these conditions, no matter how tighten the gland packing is tightend, to obtain a permanent leak-proof condition.

New stuffing box type valves which Ishida Valve Mfg. Co.,Ltd proposes, are "Twin Pack Valves." The design of the Ishida Twin Pack stuffing box eliminates these problems.
The design accomplishes this with the use of a two stage sealing system. Fig.2 shows the design of an upper and lower stuffing box gland.

Twin Pack Valves

The features of stuffing box of Twin Pack Valve,

  • 1)Complete Sealing (Perfect Leak-Free)
    The TWIN PACK design provide perfect leak-proof sealing design by clamping the primary packing box from the fluid side... By use of a clutch ⑤ and gearing ④, the primary is compressed as the stem is turned to provide a leak proof scale... The upper secondary Packing is tightened the conventional way and will prevent a stem leak under an abnormal condition where a leak occurs at the primary pack- ing...
  • 2)Long-term Durability
    The TWIN PACK design provide perfect leak-proof sealing design by clamping the primary packing box from the fluid side... By use of a clutch ⑤ and gearing ④, the primary is compressed as the stem is turned to provide a leak proof scale... The upper secondary Packing is tightened the conventional way and will prevent a stem leak under an abnormal condition where a leak occurs at the primary pack- ing...
  • 3)Easy Maintenance
    The back-seat of conventional valve tends to be prone to damege and to be unstable. To replace packing can be difficult. In the Twin Pack design, the gland packing substitutes for the back-seat, and, if necessary, the secondary packing can be easily replaced even though the valve is at an intermediate open/closed position.
  • 4)Smooth Operation
    In Operation, gland packing is clamed by the leading of a screw, so the valve can be operated more easily than the conventional design because it prevents eccentric positioning of the stem that could occur when clamped on one side.

2.Operation of Twin Pack Valves

  • (1)The primary packing of the Twin Pack valve should be tightened under these conditions:
    • 1)Before fluid runs in the lines after the construction pressure test, the primary packing should be tightened.
    • 2)At any sign of a small leak during plant operation, tightened the packing.
    • 3)At the annual plant maintenance shut down, the packing should be tightened.
  • (2)Procedure to apply pressure to the primary packing.
    • 1)For a gate valve
    • a. Open valve wide open by turning counter clockwise.
    • b. Discontinue turning when the wheel stops.
    • c. Release the lock nut to free the stopper.
    • d. Turn the step top lever clockwise 30 to 45 degrees and the packing is clamped.
    • e. Tighten the lock nut and place the stopper in the original positions.It is important to return to the initial state.
    • 2)For a globr valve and a forged valve. (1 1/2" and smaller)
    • a. Open valve wide open by turning counter clockwise.
    • b. Discontinue turning when the wheel stops.
    • c. Turn further in the same direction (counter clockwise) 30 to 45 degrees and the packing has been clamped.
  • (3)Maintenance instructions should call attention to the following:
    • 1) In case of these valves for control valves, isolation valves, or drain valves, the valves are not normally opened to the full open position which would have tightened the packing...So, during maintenance.
      Shut-down, the valve should be opened to the full open position to tighten the primary packing.
    • 2) It is good practice include the above maintenance information on the name plate of each valve.
    • 3) Any small leak is important and should not be ignored...Tighten the primary packing and also tighten the secondary packing to insure a sure seal.
    • 4) For the gate valve, do not turn the lever to the left after the primary packing has been clamped. The screw of the clutch returns to the original position and, if the lever is turned to the left, the clamped packing can become loose.
    • 5) For the glove valve and forged valve (1 1/2" and smaller), do not use a hacker(a wheel key), if the valve is opened with the wheel key, the primary packing may be closed too much.
    • 6) To replace the primary packing with new packing, disassemble the cluch from the bonnet with the tools.
  • Fig4.ゲートバルブ
  • Fig5.グローブバルブ

3.Twin Pack valves can be used on special fluids and special

  • (1)For heating media
    Downtherm A, Therm S, S-K Oil, Marlotherm, Essotherm, HTS, Hygrotherm, Fused Lead, Fused Sodium, Fused Potassium, etc
  • (2)For high pressure, high temperature steam
    Downtherm A, Therm S, S-K Oil, Marlotherm, Essotherm, HTS, Hygrotherm, Fused Lead, Fused Sodium, Fused Potassium, etc
  • (3)For hazardous gas and liquids such as hydrogen
    chloride(refer to the Yellow Twin Pack), hydrogen sulfide, phosgene, carbon monoxide, etc.
  • (4)For prevention of pollution by preventing leaks of sulfurous acid gas, acetic acid, carbon dioxide.
  • (5)For use for vacuum to a maximum 10-2mm Hg.
  • (6)For low molecular weight gases Hydrogen, Oxygen, Freon, Gas, LPG etc.
  • (7)For nuclear power plant.

4.Specifications

Twin Pack Valves are designed, the same as common valves, to conform to API 600, and ANSI B16.5 and the same pressure/temperature ratings apply. Please refer to attached tables for 150#, 300#, 10K, and 20K, standard valves.

  • (1)Nominal pressure class
  •     150#, 300#, 600#, 900#, 1500#, 10K, 20K, 40K, 63K
  • (2)Nominal bore size
  •     1/2"~36"
  • (3)Available as gate valves or grobe valves

5.Materials

  • (1)Body material for Twin Pack valves is in accordance
    with API 600. Common materials are carbon steel, alloy steel, and stainless steel. Other maetrials like monel can be supplied as required by the customer.
    Standard trim materials are 13 Cr and 18-8 stainless steel. Monel and other materials are available.
  • (2)Material for trim
    13Cr and 18-8 stainless steels, etc are used in conformity with API STD 600.
    Special material, such as Monel metal, may be used when so requested by customer, as well.