Narrow vanes in radial arrangement on the rear side – looking in the direction of flow – of a centrifugal pump's impeller. They serve to balance the axial thrust. In pumps with back vaning of the impeller, the sealing pressure is higher than the suction pressure and lower than the discharge pressure. Although the exact values differ from one pump type to another, the following rough formulae have proven sufficiently accurate for determining the sealing pressure of single-stage centrifugal pumps:

For a rated pump speed n = 1500 rpm

p_A » p_S + ²/₃ · H · s
For a rated pump speed n = 3000 rpm

p_A » p_S + ¹/₃ · H · s

p_A = sealing pressure

p_A = discharge pressure

p_E = suction pressure

H = delivery head

s = density