SUCTION RECIRCULATION 17-11
A line is connected between the suction of the pump and the bottom of the stuffing box or seal gland connection. Many pumps have a connection already tapped at the suction throat of the pump for a suction gage, but if none is available you can install one in the piping or a pipe flange if the piping is not thick enough to be drilled and tapped. Try to make the stuffing box connection as close to the seal faces as possible to insure a good circulation through the stuffing box.
Stuffing box pressure is almost always higher than the suction pressure of the pump. Liquid from behind the impeller will be circulated through the stuffing box to the pump suction. The impeller has centrifuged this liquid and the result is that the liquid going into the stuffing box is considerably cleaner than what you are pumping. In many cases you can eliminate the need for bringing in clean liquid and diluting your product.
This environment control works very well in closed impeller pump designs and those open impeller designs that adjust towards the pump volute rather than the back plate such as most Flowserve (Duriron) pumps.
You should not use suction recirculation in the following applications:
- If you are pumping at, or close to the product’s vapor point.
- If the entrained solids have a low specific gravity. In other words, they float.
- If you are using a Duriron pump or any impeller that adjusts to the back plate. You will get some recirculation, but not as much as those open impellers that adjust to the volute.
- If you are using a double suction pump where the stuffing boxes are at suction pressure.
- On February 18, 2018