Considering its a backyard fountain, I think downtime isn’t a grave concern. Certainly not enough of one to engineer in redundancy.
If its a swedish made pump you are only gonna need one baabbieee.
Post #5
FWIW
Just to clarify Sapo, my understanding is you’re not looking for design help on this just to kick around some of the potential issues that could arise so that you’ll have the right information on hand when you talk to your plumber is that correct? Things such as whether you need check valves on the discharge and that type of thing?
Right, I just don’t want to look completely clueless when I talk to the hired professionals. Also, since I am just the idea guy on this project and have very little say in hiring these professionals, I want some way to gauge if they know what they are talking about. It might not be my money, but I do want to see the project successfully completed.
Will you have an engineer involved? Undoubtedly some plumbers could handle a project like that but there an awful lot who can’t (but would try anyway).
I have a pool guy who has done big[ish] projects with fountains and waterfalls and all that. I am now getting the feeling that this might be more than he can handle as he is not an engineer. Someone suggested I contact my nearest university and get an engineering student, which I though was a brilliant idea for getting some brainpower on the cheap.
The current incarnation of the idea is actually rather simple as all the jets will be static, most of them are very low (1-2’) and the whole project is not really that big and there is plenty of room for pumps and all that right next to where we want the installation. Also, it is a new build so we are not constrained by existing structures and all that.
ETA: The tricky part is that there will be a lot of jets and I want them all to look uniform. Here the fact that they are small jets might actually be a difficulty since they are then easier to compare.
I want to believe that our guy is capable of handling it, but I would like some way to gauge his competence over his confidence. He has so far said that this is all piece of cake. My problem is that his answer to everything is “yes, that can be done” with no further explanations of exactly what and how he is planning to do. Granted, that’s what he is paid to do and as my auto mechanic says all the time, I am paying enough for a car fix, not for an education. Still, I wish I knew enough about this to know if what he wants to do is ok before the whole thing explodes.
A thought regarding the two pump approach. Lets say its something really simple like a ring of jets spewing upwards along the edge of birdbath.
If you didnt think about it at all, you’d make one half the circumference one run on one pump and the other half on the other pump. And that would be a bad idea.
If the pump pressures were not close to equal, jets on half the side would be higher than the other, looking like crap. And if one pump is temporarily down, again it looks like crap.
Now, if you get a bit smarter, you run two rings around the perimeter, with each ring running off a different pump. If pressures arent equal, its still good. And if one pump is down it still looks decent.
Is this kinda distribution something that can be done for this project?
Theoretically, I guess yes. It would mean a royal nightmare of multiple piping nets underneath, though. Plus, the walls tolerate only a maximum of space between jets before they stop being read as a continuous wall. And with one pump down among more than two, then the missing jets start reading as gaps on the wall.
This is why I would like multiple pumps running in parallel. If one is down, all jets go down a little bit but the effect holds. Also why I would like say 4 pumps where 3 are needed so you always have a spare ready to kick in when one goes down.
How will you control the pumps? Is someone going to manually turn on the fourth pump or will it be done automatically?
I was thinking manually. This is either a planned event (for maintenance) or a rare event (for failures) and this is not a life-critical installation. 10 minutes of the thing looking wonky while someone gets up and flips a breaker switch is acceptable.
Making them all uniform sounds to me like the hardest part of the project, and the part where you’d need an engineer and not just a plumber who’s done fountains a few times before. Do you have an idea what your requirement is for uniformity? Does your plumber, or whoever you hire, have a way of showing that he will satisfy that requirement prior to the work being performed?
White a university student many have the “brains” this really, really sounds like a project where you need someone with hands on practical experience in designing fountain systems.
If they’re all identical nozzles the flow will be the same through each as long as the pressure on the upstream side is the same. The pressure on the upstream side will be affected by friction, and since every nozzle will be a different distance from the original pump, the pressure can’t be the same.
Let me illustrate with a simplified example. We have a straight piece of pipe. Ten feet from the pump we have a nozzle, and 10 feet from that nozzle we have a second nozzle, and then the pipe continues on.
We send 20 gallons per minute with a pressure of 34’ of head from the pump through a 1" pipe. The pressure loss at that flow through new schedule 40 pipe is 25.2’ per 100’, so we lose 2.52’ of head getting to the first nozzle. At the first nozzle the pressure is therefore 31.7’. We get a certain flow through the nozzle based on P1 and P2. Say we engineer the nozzle for a flow of 5 gpm at an inlet pressure of 31.7’.
Now the flow through the pipe is only 15 gpm. The friction loss for that flow through the same pipe is 14.6’ per 100’, so we lose 1.46’ of head getting to the second nozzle. We started at 31.7, so the pressure at the second nozzle is only 30.2 feet. The flow will be slightly different.
A third nozzle further along will be even less, and so on. Feeding the system with two pumps on either side would help, and the larger the pipe diameter the less the frictional effects will be, but if you want all the spray heights to be the same you’ll need to engineer every nozzle separately, and then it will only work within a specific flow range, so you’ll have to add either flow or pressure controllers to keep it.
A 1/4" nozzle at 35’ inlet pressure gives a flow of 7.24 gpm but by the time we get to the fourth or fifth nozzle at 23.1’ inlet pressure the flow would be 5.91 gpm. You could try a 5/16" nozzle, and the next one might be 11/32" but they’ll all have to be as individual as a snowflake.
In an industrial setting we’d use individually engineered orifices and control valves to maintain flow. With a pump that small I might try a variable frequency drive and a pressure control loop, I don’t know. The last pump I bought was a 250 HP pump delivering 4000 gpm at 160’ total delivered head, so I don’t have a lot of experience with small systems.
Since this is purely for show, the requirement is that it looks uniform to the eye. As four our plumber, he was “chosen” because he is the guy that does this kind of work for the city. The city officials seem pretty relaxed about the whole deal which is what’s panicking me.
Thanks for the detailed example. It does help a lot and it has confirmed some of my hunches (I may suck at math but I am very proud of my physics intuition).
Long story short. We need an engineer. I just came back from making an appointment with the big guys. This will be my own point for this meeting. No engineer, no pretty fountain.