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On a swimming pool a 2 hp pump should have greater pressure and volume than a one and a half hp pump. then why is the pressure and the volume the same with both motors in filter mode?



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a 2 hp pump has a stronger motor it does not necessarily run a bigger pump. It sounds like in your case the pump in the old motor was just as good as the pump on the new motor. There are other considerations to keep in mind such as was the old pump a high head pump and how did the new pump compare with it in that way. A high head pump will give you more pressure. Pool hydraulics: Even if you replaced a 1.5 hp pump with a 7 hp pump you will not get any more flow out of the system than the plumbing can handle. You can only put so much water thru a 1.5" pipe. One soultion would be to change the plumbing to 2" or even better 3". However that is impractical. The 2 hp pump is going to cavitate and will have a shortened life because it is working harder than it was designed to. Replacing an older style pump with the new more efficient pumps of todays designs needs to be done carefully. You need to do some homework on the hydraulics of your particular pool. But that is a lengthy discussion and complicated for a novic. Bottom line in replacing old pump with new - - - downsize with the new pump - selecting a lower hp rating like - a one hp or even a .75 hp would work more efficiently than the 2 hp. And it would save you in electricity costs and pay for itself within 2 yrs.