How to Determine the correct cross section of Gland Packing
It is very important to choose the correct size of gland packing to form an effective seal. Firstly;
- Measure the diameter of the shaft.
- Measure the ID of the Gland or Stuffing box.
- Subtract the shaft diameter from the Gland I.D. Then divide your figure by 2.
i.e. (Gland I.D (50mm). – Shaft Diameter (25mm)) ÷ 2 = 12.50mm (1/2”) cross section.
This is the recommended Cross section to be installed
Preparation of Gland or Stuffing box
It is very important to prepare the stuffing box to form an effective seal. Firstly;
- Shut down the unit or pump.
- Remove any used Gland Packing without damaging the shaft or housing, using a packing extractor (This can be purchased from Vulcan). IMPORTANT – Even a small piece of used Gland Packing will greatly reduce the efficiency of a new packing.
- Count the number of Gland Packing rings (Where appropriate, remove the lantern ring using pullers and then count the number of rings below the lantern ring).
- Clean the shaft and stuffing box removing any evidence of; scale, rust, dirt etc. Remember, the cleaner the stuffing box, the better for re-packing. Check, preferably by hand/touch, for any signs of damage i.e. Shaft wear, scoring grooves etc.
- Spray or wipe the shaft an gland with a silicone grease.
Installation of Gland Packing from a length form
- The exact length of required material is cut from the coil. Spirally wrap the material around a rod of the exact diameter to the pump shaft to be sealed.
- Cut the required number of rings (cleanly to obtain good square joints) by making a straight cut along the shaft. When removing the rings from the rod, do so, by slipping them off without opening the rings.
- Place the first ring over the shaft by opening to an ‘S’ shape, to ensure that any bending effects are spread over the whole ring and that there is no deformation of the cross section.
- Partially enter both ends of the first ring together into the stuffing box before inserting the remainder of the ring and then lightly bed into the bottom of the stuffing box.
- Repeat steps 1 & 2 with the remaining number of rings ensuring that each ring is firmly seated and that the joints are staggered by a minimum of 90 degrees (Where appropriate, ensure the lantern ring is correctly positioned). IMPORTANT – failure to position the rings at alternating 90 degree angles will result in a leak path forming and thus, failure of the system. It is also vitally important that each ring is fitted individually and not as a full set. Ensure that the shaft turns freely after fitting each individual ring.
- When the correct numbers of rings have been fitted, tighten the Gland nuts until the shaft is lightly gripped. Then tighten the gland nuts by hand, only. Again, check that the Gland turns freely.
Start-up and break in of the Gland Packing
The purpose of the Gland Packing is to control leakage, not prevent it. There must be a level of leakage for the Gland Packing to perform properly otherwise, failure will occur. Firstly;
- Reconnect and Gland and/or Pump flushing arrangements and start-up the Pump. Allow 10-15 minutes of generous leakage, as this will increase the Gland Packing life.
- Begin to tighten the nuts gradually by one sixth of a turn. Continue to tighten, by one sixth of a turn, at 10 minute intervals until leakage has been reduced to an acceptable level. IMPORTANT – do not over tighten.
- The ideal leakage rate is reached when any subsequent tightening of the Gland nuts causes an heat build-up (usually within 45 – 60 minutes)
- Occasionally re-check the Gland Packing for any signs of excessive leakage, heat build-up and/or other failure mechanisms. Re-adjust the Gland Packing as necessary.
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