Well pressure tank Q

I'm getting the well system in my home back in working order and breaking it off the household feed for use as outside water sources and irrigation.
I have an existing pressure tank that I can use, 36 gallon Sears 390.29161 - I need to test the air bladder which I'm in the process of tonight.
In the event that I've got the same air pressure in the morning that I had when I refilled the air I'll need to know the PSI that the bladder should be filled to while OFF SYSTEM and no water in the tank.
Anyone have any ideas how much pressure should be in them?
I'm hoping to not have to replace the tank and to avoid that expense and to only have to work on a new jet pump. Replacing both would double the costs.
As for the pump, I'll be using a 1/2HP convertible jet pump. Pretty standard stuff and the lowest HP I seem to be able to get. I really shouldn't need more than 10GPM at any given time.
BTW, irrigation would be a drip system covering the flower beds and possibly a small veg garden, just in case you're wondering.
Alot of rambling for a little question (how much pressure in the air bladder, that is) but I figured I'd explain what my needs are and what I'm doing just in case anyone wanted to kick further input.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
With the tank empty, you want to set the pressure to be a tad less then your pump cut in pressure. In my case, I have it set to 24psi, and my pressure regulator cuts in at 25. You don't want the bladder pressure to be higher then the pump cut in pressure, because if it is, then when the bladder hits the bottom, you will have a sudden loss of pressure before the pump kicks in. The resulting surge can jar your pipes, though in most cases it doesn't hurt much.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks Ook,
That's exactly what I needed. Though I should have figured that's what it should be set at. Makes perfectly good sense to me. :)
Ook wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sometimes when I hear out a question and its end purpose, I like to start from the purpose.
I can't see all you're doing for doing drip irrigation on a flower bed and a small garden. Won't be anywhere near 10 GPM. The current pump and reservoir tank should easily handle that and the house needs. Seems to do fine here without all the aids you seem to need. No drip, manual surface irrigation here.
Find interesting the air pressure thing. My reservoir tank relies on the elasticity of the bladder for pressure when the pump is not running. Also aiding is the pumphouse is uphill from the house and rest of my irrigated area. Maybe you're pumping uphill to the flower bed etc. But, should be of little consequence since the flow rate is so small. Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are you sure it's bladder elasticity, and not air pressure behind the bladder, that is giving you pressure? A bladder can't hold pressure - it would burst. Bladder tanks rely on the air behind the bladder, not the elasticity of the bladder, to maintain pressure when the pump is off.
I irrigate a 1/3 acre garden and yard with a small pump. The problem with 1/2 horse pumps, especially the cheap ones, is that one day you decide that drip irrigation won't work for some odd patch of garden, and you go and hook up a couple of impact sprinklers. That is when you find that your 10GPM pump only pumps 10GPM at ideal conditions that don't exist in the real world. And having been through several different 1/2 horse pumps, I can testify that they are not all equal. My Gould JRS5 is an excellent pump. I also have an el-cheapo Flowtec that I got from Home Depot that is a worthless piece of junk. Today, I use a Star 3/4 horse pump. I don't need the theoritical volume it can pump, but the difference between the smaller pump and the bigger pump is that it takes 30 seconds for the big pump to fill the tank and bring the system up to pressure, where the 1/2 horse pump took a couple of minutes. Also, the Star maintains volume at 55psi, where most cheap 1/2 horse pumps barely trickle at higher pressures. You put them under load, and the small pump runs constantly, and the big pump cycles at a comfortable rate.
</soapbox>
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ook wrote: <S>

Your soap box may have just talked me up to the 3/4. Granted I'll be using it to water stuff for the most part, but there will be a need to do more from time to time.
At the very least I'll check elsewhere for a pump than at Lowes.
Oh, and some pressure tanks that use a diaphragm are indeed pre-pressurized from the factory to specs. They don't have any way however to re charge the tank and fill the other end with air.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Heh - I understated how much I love my 3/4 pump! When that bad boy kicks in, it's quieter then then my 1/2 horse pumps (go figure?), and the pressure ziiipppss right up to cut off. That was the first different, and it was immediately obvious. The 3/4 zips right up to cutoff, while the 1/2 runs and runs and runs. The Star pump maintains high volume at higher pressure, so it fills the tank up much faster. The other pumps loose most of their volume at higher pressure, which is why it takes them so much longer to fill the tank.
It's a Star Systems 3/4 pump - I looked up the specs online, and it compared close to the Goulds, and was way ahead of the Flowtec. The Flowtec pumps are cheap bottom end pieces of junk. Avoid at all costs. Goulds are very good, and have the highest capacities of all of the ones I looked at. The Star was a somewhat close second place. IIRC, the Goulds 1/2 horse pumps more then the Flowtec 3/4 horse. I bought it at Coastal Farm supply. Home Depot and Lowes here only carry the cheap low end junk pumps.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.