Pressurizing water distribution system w/o tanks

[s0eebuch]

All,

Here is the situation: We have a rural water system which consists of a well, one lead pump, one lag pump, one 250K gallon aboveground storage tank, a pneumatic control valve, and underground piping.

I need to take the tank out of service for maintenance. In the interim (about 3 weeks), I need to keep the sytem up to pressure (a minimum of 20 psi).

I would like to bring in temporary storage, such as a bladder tank. The operations manager would like to change the pump controls to have the pumps run continuously and discharge excess water to drain via a pressure relief valve.

Has anyone had any experience with 'tankless' water systems? Any items I need to be aware of? We've never done anything like this, so any basic direction would be great. I don't like the op manager's idea because it would waste water. On the other hand, bladder tanks pose a security risk and take up a lot of space.

Thanks in advance!

 

[BigInch]

You probably won't need the bladder tank for short term operations, unless your pumps can't get to the maximum demand (flowrate). How do you know? If your pressure does not fall below 20 psig at any time, WHEN the tank is blocked off and bypassed, you won't need a tank.

I also don't see a necessity to run the pumps continuously. Set the controls so that a pump turns on when the pressure lowers below 20 psi. Your pressure relief is there for pressure relief, not for continuous flow. Depending on the type of pressure relief valve you have, it may introduce pulsations or even surges into your system by using it in a continuous manner.

The proposed operation is wasteful of both water, power and could even overheat the pumps if the flow through the relief valve is less than the pump's minimum flowrate.





BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[thewellguy]

YOu could use a bladder tank however, you need to maintain a minimum of one minute run time on all of the pumps. Depending on the size of the well pump is is only supposed to be started across the line 4 times an hour and the booster I beleive it is less then 10 starts per hour. I would recommend that you look into a Vfd that can run the well pump and feed directly into distrobution. You could just run the pumps and all the time and put a pressure releif valve on the main but this will waste alot of water.

 

[FACS]

We install constant pressure systems to eliminate the need for large storage tanks. Maybe as an alternative, you could look at converting the system to Constant pressure and move toward a smaller tank.

Since you are shutting down anyway, maybe it's something to consider.

3 weeks sounds like a long time.



Charlie

http://www.facsco.com

 

[zdas04]

Weatherford makes a constatnt pressure valve that takes a side stream to recirc. I've used them in situations where the demand was variable but the desired pressure was constant. They work much better than using a PSV (which is not intended to maintain a constant pressure).

In your case the big issue would be where you go with the recirc, any chance of being able to put it into the tubing/casing anulus on the water well to keep from losing it?

David

 

[BigInch]

zdas, Isn't it lost if he pumps it back down the well?

Wellguy, VFD recommendation seems premature and why run the pumps all the time? Are you really recommending blowing excess flow through a pressure relief?


BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[thewellguy]

zdas04, Pumping the water back down the well is not a good idea. You could damage the pump or wire. Also submersible pump motors require a minimum flow past the motor to cool it so the re curc water could disrupt that.

Biginch, I do not recommend blowing the excess off through pressure reliefs, however I have seen it done on many occasions on a short term basis.

I am not sure if a vfd is the right answer with out more info. It depends on the system size and usage. I was just suggesting options. I have installed vfds on several small systems so that they can avoid the expense of large storage tanks. It may be a good fit or not.

 

[SteveWag]

I have done this many times with above ground pumps, not with well pumps. As you say you have a lead/lag situation, do you have two wells, is this a shallow well situation? If you have access to the suction pipe(s) I would install a Back Pressure Sustaining valve, about a third of the discharge size, connected from the discharge to the suction. This will let you run the pump, and the discharge pressure will be set by the valve setting. You may be able to throttle the pump as well. You will not loose any water, but when the system flow drops to zero, 100% of the flow is recycled. The recycled water will begin to heat. To eliminate the heating, I open a 3/4 inch valve somewhere in the system and direct this flow to a drain. I have a tapped hydrant cap and use a hose to lead the water to a storm drain, if available. You will not have fire protection. Notify the local fire people as to the beginning and ending of the temporary pumping. (My rant): I am tired of reworking municipal pump stations for that have been designed to fill a tank with no provisions for taking the tank out of service. Don’t these guys live in a real world? The piping/mechanical layout MUST allow for removal of the tank from service.

 

[zdas04]

I work in Oil & Gas, and our wells tend to have a tubing string within the casing string. In this configuration, you can send the excess production down the tubing/casing annulus (on wells without a packer) which would recover the recirc liquid, not interfere with the pump production, and actually aid in cooling.

I've seen some residential-water wells where the pump and production tubing are lowered into a casing and in that case I don't know why you wouldn't be able to recycle back to the casing. It sounds like municipal wells have a different configuration. If so please disregard my inappropriate suggestion.

David

 

[FACS]

I've seen some residential-water wells where the pump and production tubing are lowered into a casing and in that case I don't know why you wouldn't be able to recycle back to the casing. It sounds like municipal wells have a different configuration. If so please disregard my inappropriate suggestion

Many municipal wells are larger versions of residential wells. There is a well casing extending through the water table. Right below the frost line is a Pitless Adapter. It might be a sealed spool or drop fitting of other design. In anycase, it is possible to dump water over the spool or past the drop fitting, but then you are dumping water on top of these units, and they have wires and ports that you would constantly be pouring water over, and they were not designed for that.

Of course, we don't know if the OP is in a building or using pitless wells.

For the people that wanted to recurculate water back into the well, I designed some drop fittings that are installed under the spool, and then piped down to the water level instead of a free fall. You can't just add a pipe to these wells, the spool and motor/pump still have to be pulled out.



Charlie

http://www.facsco.com