Why are the caps of pumps that rotate clockwise threaded in the opposite direction?
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The pump that rotates clockwise should have its cap aligned properly, right? Because it rotates tighter the more it turns in that direction; I’m not quite sure about this.
We often talk about having spare caps; I’m not sure if that’s the same thing as what I’m referring to. The reason is that it spins tighter and tighter; otherwise, it would fall off.
Some set-screw bolts have a section of left-handed thread on their head (with a diameter smaller than that of the main thread) to facilitate removal, allowing the bolt to be unscrewed in the opposite direction. If they are all dextrorotatory, it will not have this effect. I wonder if this function is the same as the one mentioned by the original poster?
This is related to the rotation direction of the pump when it is designed. Generally, when looking at the pump from the side of the impeller, it rotates clockwise. The cap on the impeller is designed to prevent loosening, and its tightening direction is the same as that of the pump’s rotation direction; therefore, in this type of pump, the threads are reversed. If the pump rotates counterclockwise, then the threads are in the correct direction. In simpler terms, the question raised by the original poster is this: if the cap doesn’t move, and you turn the pump shaft in the direction in which the pump rotates, does it get tighter as you keep turning it? It works on the same principle.
It’s simple – it’s to prevent loosening! Because it is not possible to install anti-loosening devices or anti-loosening washers in these areas. These pumps cannot be reversed!
It is to prevent loosening, but a anti-loosening washer should also be added in the impeller nut (cover nut).
During operation, the force exerted on the cap by the medium acts in a direction opposite to the direction of rotation; the thread direction chosen to be opposite to the direction of rotation is intended to prevent the cap from coming loose due to the force exerted by the medium while it is in use.
I think ddfmy is right; based solely on the rotation of the impeller, it should be the case that the tightening increases as it rotates, and the force exerted by the medium also needs to be taken into account.
Regardless of the rotation direction of the pump, the pump shaft may have threads of both rotation directions. If the pump rotates clockwise, the lock nut tightened from the drive end should be left-handed, while that at the far end should be right-handed, so that it becomes tighter as it rotates more. Conversely, if the pump rotates counterclockwise, the back cap on the drive end should be right-handed, while that on the far end should be left-handed.