## Info

Glands are usually made of bronze, but cast iron or steel can be used for all-iron pumps. When iron or steel glands are used, they are normally bushed with a non-sparking material like bronze.

Leakage and Power Consumption The basic operating parameters for compression packing are the PV (pressure X velocity) factor and the projected bearing area of the assembly. Together they determine the rate of heat generation for the system. Some leakage of the product being sealed or of the packing lubricant is necessary to keep the packing from burning up or scoring the shaft sleeve. The minimum values for leakage at different packing pressures are given in Table 4. Flexible graphite and carbon filament compression packings can be used with reduced leakage rates, or in dry, gas-tight pump stuffing boxes, as the developed heat is dissipated through the packing and pump housing.

The exact pressure P between the shaft sleeve and the packing is a function of the pressure distribution over the length of the packing and the axial loading from the gland. For ease of calculation when determining the PV value, the gage pressure of the liquid at the packing is multiplied by p X the packing ID X rpm. The heat generation at the packing can then be estimated as fp2PND2L

where Q = heat generated, Btu/min (W) f = coefficient of friction

P = liquid pressure at packing, lb/in2 gage (bar) N = shaft speed, rpm r = sleeve OD or packing ID, in (m) L = sleeve length covered by packing, in (m) C = 12 (60 for SI units)

J = mechanical equivalent of heat = 778 ft • lb/Btu (1 N • m/s • W)

The coefficient of friction for various packings at a pressure of 100 lb/in2 (6.8 bar) is given in Table 5. The heat generated by the packing must be removed by the leakage through the packing.

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