Installing compression packing into stuffing boxes is often not carried out correctly, reducing the life of the packing and causing unnecessary leakage. This two-part blog gives tips to follow for correctly installing compression packing, thereby ensuring a trouble-free installation and maximum packing service life.
Tip #1: Select the optimal packing style.
Too often, when installing compression packing, the incorrect packing is selected and installed. A variety of factors need to be considered including the following:
Type of equipment (i.e., pump, valve, etc.)
Condition of equipment
Physical and chemical characteristics of the medium
Temperature and pressure of the medium
A common mistake when installing compression packing is to use the same type of packing that was used previously. This may propagate a selection mistake. The factors listed above should all be considered and the optimal packing for the application at hand selected.
Tip #2: Determine the correct packing cross-section.
Choosing packing that is too small for the stuffing box will result in an unacceptable level of leakage. Similarly, choosing packing that is too large will be difficult, if not impossible, to install. A mistake often made is when converting metric measurements to imperial, and vice versa. For example, 1/2” is 12.7 mm, not 12 mm. Installing a 12 mm packing into a 1/2” stuffing box will cause an unacceptable level of leakage.
Tip #3: Calculate the correct length of the packing rings.
When installing compression packing into stuffing boxes, there are three different diameters one could use to calculate the length of a packing ring:
The shaft diameter (also called the inner diameter or I.D.)
The stuffing box housing diameter (outer diameter or O.D.)
The middle diameter (M.D.)
For calculating the length of a packing ring, the shaft diameter is too small (resulting in too short a packing ring), the outer diameter is too big (resulting in too long a packing ring). Only by using the middle diameter will you be able to calculate the correct length of a packing ring. Where the middle diameter is unknown, it may be found by adding the inside and outside diameters and dividing by 2.
Once the middle diameter is known, the packing ring length can be calculated by the following formula:
Length = MD x 3.14
Due to the behaviour of braided packing once installed, packing rings usually have to be cut to a slightly longer length than that given by above formula.
Canada Rubber Group Inc. (CRGI) supplies high quality compression packing made by Teadit. Compression packing that we stock service a wide variety of equipment and applications. To find out more about these fine packing products, please contact our sales department at email@example.com.
Next week: We continue our series on installing compression packing with Part II: Cutting and installing packing rings.