You only need a few 2 - 5 PSI to prevent coking. alternatively set the plan 62 steam quench with a small amount of steam visible through the bushing if laby design or drain. too much steam can lead to condensate travelling along the shaft into bearing housing. Do not use steam at high pressure because you may blow the seal.
I agree with flexibox. We only adjust our steam quench visually, not by pressure. The smallest wisp of visible steam is sufficient. Any more can lead to bearing problems.
Visual wisp is best; 1-3 psi if you want to put a pressure rating on it. Since most gauges are either broken or unreadable, you should rely more on the visual setting.
