520' well; what size pump do we need (1.5hp or 2.0hp)?

[Dan520]

Hi, we just got a new well installed. They had to go to 520' to get about 6 gallons/minute. The installer is suggesting we go with a 2.0hp constant pump even though he originally said a 1.5hp constant pump was enough. We will only be using the well for irrigation (~.5 acres) and topping off the pool. Can you please advise whether we really need a 2.0 hp pump. Also, they said since we were only able to get 6 gallons / minute, we would need to stagger the irrigation and let the well recover for about 15 minutes for every zone. Thanks

 

[Valveman]

What is the static water level?

 

[Sponsor]

 

[Dan520]

What is the static water level?

I think it is 300

 

[Valveman]

With a pump set at 520' and a static of 300' you have 300+ gallons stored in the well. At 6 GPM output you can run for at least an hour at a time. You do not need a variable speed pump with a 6 GPM well. The contractor just makes a lot more money on those variable speed things, and they don't last very long, which is why they push them on you. It will take a 7 GPM, 2HP to still build pressure when the water level is at 500'. And if you are careful how you irrigate you maybe able to get by with that. But I would just use a regular pump and a 40-80 gallon size pressure tank, not the variable speed thing. A pump that deep will be expensive to maintain, and a variable speed will just make it 4 times more expensive.

Personally I would use a 1HP, 5GPM pump and a cistern storage tank with a booster pump. This will take a lot of wear and tear off the down hole pump, and allow you to irrigate and use water anyway you want. The waiting time will be during off peak hours where the cistern will have time to refill.

 

[Dan520]

thank you for the detailed response. we talked w our guy again and decided to go with the 1.5 hp pump but no storage tank. we just have to let the well recover in between each zone

 

[Valveman]

And you are listening to someone who is trying to sell you a variable speed pump for a 6 GPM well?

A 1.5HP, 5 GPM pump will supply 5 GPM at 50 PSI even when the water level is at 500'. Most yard sprinklers will do about 3 GPM. So if you try to run two at a time you will have low pressure. If you only run one at a time the pump will cycle on and off.

5 GPM is needed for the house. So without a larger pump you will not be able to run sprinklers at the same time as the house is using water. With a storage tank and a larger booster pump you would be able to use as much water as you want and all at the same time if needed.