An addition to my first post yesterday, March 31...I am trying to decide whether to use 3/4" or 1" polyethylene underground pipe.
Thanks,
Bob

For the relatively small difference in cost, I would go with the 1" poly. You will not lose much pressure by doing this. Also, nothing worse than going with a smaller pipe only to find out after you have it in that you do not have the pressure that you had expected. Once and done.

bg,

Are the hydrants going to be just hoses or actually uses to irrigate areas? The first information you find out is what flow rate you are getting from your main line. You already know the pressure. Install your tee at the mainline then install a ball valve shut off. Attach a small length of your poly line and time filling up a 5-gallon bucket. Calculate your gallons per minute source. That flow rate will be at each hydrant and if you use two hydrants at the same time, each will have half of that rate. If you have all 4 hydrants working, each will have a quarter of the total flow rate. Friction loss along the pipe increases as the pipe diameter gets smaller. For over 400 lf you should use a 1 1/2" diameter to minimize pressure loss. This will decrease the noise of the water traveling thru smaller pipe diameters and eliminate water hammer when valve are shut quickly. This is because the water velocity in the pipe decreases as the pipe diameter increases. The 13 ft vertical drop to the last hydrant will increase pressure by 6 psi which is good but not alot. All these comments are general in nature and not to be considered exact. JMHO anyway. Aloha

Thank you all for your advice and info. I have been doing some calculations over the last few days and came up with the same solution as you - will go with 1".
Bob