You are not logged in.

Dear visitor, welcome to SPRINKLER TALK FORUM - You Got Questions, We've Got Answers. If this is your first visit here, please read the Help. It explains how this page works. You must be registered before you can use all the page's features. Please use the registration form, to register here or read more information about the registration process. If you are already registered, please login here.

swegman

Active Member

1

Sunday, May 30th 2004, 4:41pm

Low Pressure When Irrigation System is Running

I have a well that is producing 30 gpm. This well is supplying water for the geothermal HVAC systems in my house (I am on public water for all other uses). When the HVAC systems are running, the water flow is approximately 18 gpm, and the pressure is approximately 40 psi. The relay on the storage tank is set to turn ON the pumop at 40psi, and to shut OFF at 60psi.

I had an irrigation company install an irrigation system this past week. The irrigation company used a combination of Rainbird 1812 PRS spray heads and 5012 rotors. As a side note, the designer had spec'd Toro 570 heads, but the people that installed the system used the Rainbird heads. I don't know whether this makes any difference.

On Friday, they powered up the system, and it is not working well. When the irrigation system is running, the water pressure drops to 35 psi, which is insufficient to raise the spray heads the full 12 inches (they raise perhaps 4 inches), and the water coming out is more of a pissing than a speay. The operation of the HVAC equipment does not appear to be affected; they continue to operate without any change in flow rate.

The well pump (a Grundos pump) is approximately 180 feet down the well, in the backyard. My property is on a slope. The storage tank, which is in the basement, is approximately 15 feet above the top of the well casing. The irrigation heads are approximately 10 to 18 feet above the storage tank (depending on the location of the particular irrigation head).

I have verified that when the HVAC systems are not running, the irrigation system works well. Thus, I have concluded that there is a pressure problem. The installers indicated that they will "go back to the lab" to figure out a solution, but I would like to see what people here think. I see three solutions. The first is to create an interface that shuts OFF the HVAC systems when the irrigation system is running. This solution is not optimal, because I have 11 zones, meaning the HVAC systems would have to shut down for several hours, which would raise the temperature in the house. The second solution would be to install some sort of pump to increase the pressure. However, this would likely be expensive, and I am not certain where the pump could be installed that would be away from the elements, close to an electrical supply line, and not create noise when it is operating. The third solution (that I see), would be to change the heads in the system to heads designed to operate under low pressure conditions. Are there such heads? Would the Toro heads (which the designer called for) have been better than the Rainbird heads? Would there be better heads still?

Finally, are there any other solutions that i may not have thought of yet?

Thanks
Steve

bobw

Advanced Member

Posts: 101

Location: Canada

2

Sunday, May 30th 2004, 6:50pm

Boy, you've got an interesting situation. I don't think that you're going to get a whole bunch of relief by changing head manufacturers, especially at this point in time as the distance between heads is pretty much established. As you pointed out, the system seems to work fine when the HVAC system isn't pulling pressure from the system. The optimal solution would be some form of pressure tank after the HVAC and before the irrigation system to help maintain pressure. No matter what you do, you are going to have issues due to the wide fluctuations with pressure to the irrigation system. If you adjust for the low pressure, then when the HVAC isn't going, the water will spray too far, etc.

A couple of ideas....

I'm not really knowledgeable about pumps, but would it be possible to change your relay on the storage tanks to come on at a higher pressure (say 50 instead of 40?). At least you won't be starving the system for pressure when the HVAC is running, and this would give a narrower range of operating pressure. The downside would be that your pump will run more often to keep the pressure in the narrower range.

Another thought is that the Rainbird heads all come with a number of nozzles to adjust distance vs. pressure. Some judicious renozzling could give you some better results, but not much if the heads are only popping a few inches.

Other than that, you could try to get your contractor to create some more zones and move some heads off of the existing ones so that you don't need as much pressure to get them to pop....

Good luck...

HooKooDooKu

Supreme Member

3

Tuesday, June 1st 2004, 6:35am

I don't think a change in heads is going to get it, and given that you already have 11 zones, breaking the existing system in to more zones doesn't sound too desirable either.

Because you say the system works fine with the HVAC off, I think you are right about the pressure problem. I suspect that where ever the 30gpm spec from the pump is coming from does not mean 30gpm @ 40-60 psi needed to run an irrigation system (i.e. you can get 40psi OR 30gpm but not both).

The only "simple" solution I can see to run both as the same time is installing another pump for the irrigation system. I don't know if it's possible, but perhaps all that is needed is a "booster" pump so that you can take the 12gpm (or less) that should be going to the irrigation system and increase it's pressure. The only question I have about that is weither or not the HVAC system still has all the pressure it needs when the existing pump is going at max for both.

The only other thing I can think of is your idea of shutting off of the HVAC. Can you solve your issue of the HVAC being shut off by irrigating just before day-break and only irrigating 2 zones per day?

drpete3

Supreme Member

Posts: 375

Location: USA

4

Tuesday, June 1st 2004, 9:53am

I dont know either but i am suspicious that a booster pump is the answer and I think it might cost another couple hundred dollars. I think it is possible to install a booster to come on when pressure drops below 40 and to turn off at 60 psi, which is what would happen when the hvac comes on and goes off while the irrigation system is running. The other option is to install smaller nozzles on your rotors which will decrease the demand for water from your irrigation system. The problem there is your pump will start cycling whenever the hvac system is off.
Thanks,

Pete

drpete3

Supreme Member

Posts: 375

Location: USA

5

Tuesday, June 1st 2004, 11:49am

My opinion also is that your company should have seen this problem ahead of time. I you are designing a system and you have a 30 gpm pump but you know that 18 gpm will be needed at times for somthing else then you have a problem. The problem lies with do you design for 12 gpm or 30 gpm. in the case of 30 gpm then obviously you will be under supplied at times. With the 12 gpm as I stated earlier your pump will cycle on and off and theat will wear out your pump.
Thanks,

Pete

swegman

Active Member

6

Tuesday, June 1st 2004, 5:38pm

I checked with Grundfos today, the maker of the pump in the well. According to them, at 32 gpm, the pump will produce a pressure of 35 psi. As the flow rate decreases, the pressure increases. It is not possible to increase the pressure from the pump beyond the 35 psi at a flow rate of 32 gpm.

Unfortunately, the storage tank in the basement is approximately 10 to 18 feet lower than the heads. Thus, the water flow has to fight gravity. In addition, the supply lines to the heads have bends (the lines are not straight). This all serves to lower the pressure at the heads. As a result, I don't know what the actual pressure is at the heads. I wonder if this can be measured?

I looked over the original proposal, and note that the designer had spec'd Toro 4" inch pop-up heads (570 sprays), but that the installers used Rainbird 1812 and 5012 12 inch pop-up heads. Could this really make a difference? The installers said they were concerned that the 4 inch pop-up heads would not spray over the shrubs as they grew, and thus used 12 pop-up heads.

Steve

HooKooDooKu

Supreme Member

7

Wednesday, June 2nd 2004, 6:59am

I doubt the bends in the lines is really a problem. Your real pressure stealers are backflow preventer (doesn't sound like there is a need in this system), valves (you'll lose around 5psi), elevation (another 5psi for that 10-18foot difference) and friction losses in the pipes (you have to know pipe size, length, and flow rate through the pipe). As an example, 10GPM through a 1" Sch 40 PVC will have a pressure loss of about 2.5 psi per 100ft (an elbow is usually equal to adding 1-2 extra feet of run length).

swegman

Active Member

8

Wednesday, June 2nd 2004, 5:07pm

I do have a RPZ valve, along with an in-line filter. The valves are Irritol 2400TB. 1 inch pvc schedule 40 is used up to the various pipes. 1 inch Poly pipe is used from each valve to the heads. Flow rates, depending on the zone, vary from about 5 gpm to approx. 12 gpm (if I recall correctly).

swegman

Active Member

9

Saturday, June 5th 2004, 7:50am

The irrigation company is coming back to the house on Monday to look at the system. Over the telephone, the guy suggested it may be necessary to install a booster pump. I suggested trying different heads first and possibly changing the zoning.

He indicated that the first choice for locating a booster pump would be in the basement, after the pressure tank. Since my basement is actually a lower level, complete with bedroom, I am concerned about the noise of such a pump. Just how noisy are booster pumps? Anything else I should be aware of with booster pumps?

Thanks
Steve

drpete3

Supreme Member

Posts: 375

Location: USA

10

Monday, June 7th 2004, 5:07am

I have tried to get info about boosters in the past but with little luck. One question I have is is hard on the first pump to have a second pump connected in line? I will be curious to hear what your company has to say. Keep us posted.
Thanks,

Pete

Rate this thread