Need to upgrade my ancient Galv tank

[sbeausol]

I'm one year into a new house we bought that was built in 1971.  Water is served from a well that I don't have a lot of specific info on.  In 2010, there was a 1/2 HP Goulds submersible pump installed set at 300' using 1" poly.  I spoke to the installer and the only extra detail they could give me was that when they shocked the well and flushed it all day, they didn't come close to running out of water.  When someone is taking a shower and nothing else, the pump kicks in at what looks like 30 PSI and runs for 45sec to hit 60 PSI.  During a typical shower the pump kicks in 2-3 times.

Inside the house I have a harvard mark 10 tank that is as tall as I am ~70", and the pump installer tells me it is an 80 gallon galvanized tank, likely installed in 1971.  It is in need of replacement soon.  I'm told I can replace the current tank with a 20-30 gallon amtrol tank which would suitably replace the current tank.  The house is a 3 bed 2 bath with two adults and a child right now.  If things work out, we will hopefully have a second child in the coming years.  I have plans to remodel the master bath, and the wife has mentioned the possibility of adding a few shower heads in the new bathroom.  As I've been reading on the topic, I came across the CSV and I would like more info, so here are my questions. 

1)  Using the methods for estimating demand, it seems like my current demand would be about 9-10 GPM.  Should we go with an extra shower head that load could move up to somewhere around 12-15 GPM.  With my current pump, can I meet that demand with the CSV?  Can I meet it with the traditional pressure tank? (I'm guessing no)

2)  Based on my current demand, can a CSV work for me with the recommended 4.4 Gal tank?  It seems like the CSV system is limited by the output of the pump in the well, or alternatively would require a larger than 4.4 gallon tank? 

[Cary Austin]

A ½ HP pumping from 300’ won’t deliver much water.  It could even be a 5 GPM pump at that depth.  But it doesn’t matter how deep the pump is set, what matters is the pumping water level in the well.  Even though the pump is set at 300’, it is only lifting from the actual water level in the well.

The fact that the pressure still hits 60 and shuts off the pump when a shower is running means that the pump can deliver more than you are using.  But if you add extra showerheads, that may no longer be the case.

A CSV can control the flow from the pump to match the amount being used.  This would keep the pressure at a constant 50 PSI for as long as the shower is running, instead of dropping to 30 and spiking at 60 several times during a shower.  50 PSI constant will seem like much better pressure in the shower than when the pressure is bouncing between 30 and 60.  However, the CSV can only do this if the pump is large enough to handle the amount of water being used.  If the pumping level in the well is only like 80’ deep, then a 10 GPM, 1/2HP pump can supply a lot of water.  The deeper it is to water, the less the pump can supply.  I would test it out by running enough hoses to keep the pressure at about 50 PSI, then measure how many GPM you are getting in a bucket.

If the pump can supply enough water, then the CSV with the 4.5 gallon tank is all you need.  Adding a larger tank will not help, and will actually make the pressure problem worse, as the pump just sees the big tank as another demand it has to fill.

The Pside-Kick kit with the 4.5 gallon tank cost $399.00 including freight.  You can’t purchase a regular size tank for that, and the CSV will work better than a room full of pressure tanks.