How to Start All Municipal Pumps with Flow Test?

12/20/2021

We have an oil storage warehouse project requiring a ceiling density of 0.60 gpm/sqft over 3,000 sqft.

This is basically 30 sprinklers using 1,900 gpm (sprinklers), and 500 gpm (for hoses).

The municipal system is set up with three pumps that run sequentially based on residual system pressure. Each pump is larger than the last. We require Pump 3 to be in operation in order to get the required flow and pressure.

We have conducted a flow test flowing two hydrants, and have not been able to kick Pump 3 into action.

Assuming a K16.8 sprinkler has a 3/4" orifice, 30 heads would only equal a 4" diameter opening. If we can't activate the appropriate pump by opening multiple hydrants, how will we be able to achieve the required flow during a fire?

Has anyone encountered a supply system like this before?

I know that a tank and pump is a solution, but I'm looking for other options. Thanks.

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18 Comments

Dan Wilder

12/20/2021 06:34:42 am

So many questions to even start with guidance on this and you'll likely get the "Hire a professional" follow up as well.

First, going to need more info on the 3 pump ratings and "ON" pressure settings. I am assuming these are setup in parallel meaning that there is a fair amount of water (GPM) flowing prior to the third pump even getting a chance to turn on. What is the site design (looped, dead end runs, a mix of both) and what is the current water supply (tank/municipal supply/both).

When you are flowing the hydrants, are you flowing a single 2½" port, both 2½", the pumper port (4"-5" depending on AHJ) or all three? What were the results of the test flowing two hydrants?

In this case, I would recommend opening at least the pumper connection for the furthest hydrants, while pressuring the next hydrant on the line until you reach the flow that activates the 3rd pump. This may mean flowing 3 hydrant with a pitot on the 4th or it may mean 6 hydrants with a pitot on the 7th. Opening all three ports may be warranted, but most companies don't have that amount of equipment readily available to accommodate.

I am not understanding the # of sprinklers/orifice size compared to the outlet size of a hydrant....there is no correlation between the two and the method to obtain flow/pressure results are different as well (one is a demand calculation, the other is a performance test which more closely mimics a supply calc). With a supply like this, adding another pump seems premature and unneeded, keeping the water supply available for the duration needed (2-4 hours) at +/-2400 GPM per minute does seem more the issue to be resolved.

Mike L

12/20/2021 08:14:46 am

If I'm understanding the situation properly, the municipal water supply has (3) pumps in series that activate as the pressure demand requires them to. That being the case, if your sprinkler demand is such that the municipal system does not meet your demand, then your system must include the necessary components to meet the sprinkler demand.

Flowing the hydrants simply tells you what the water supply can provide. If your system flow demand does not activate the third municipal pump, then your system needs to have its own pump to meet the calculated demand.

This is an off the cuff response. As Dan has noted, a lot more information of the system architecture is needed to come up with viable solutions.

Jesse

12/20/2021 08:35:16 am

This actually presents a lot more in the way of questions.

Like Dan, I'm not understanding the concept of # of sprinklers with a given orifice equaling a larger orifice.

We design based on the water supply characteristics we see in the flow test. If the hydrant flow test was conducted consistent with NFPA 291 - meaning we keep flowing hydrants until we have our fire flow, it seems that you would have A) met the requisite fire flow and triggered the 3rd pump or B) not done so.

If its B, then considerations should be made to installing a stationary fire pump at the facility.

12/20/2021 08:36:04 am

It's a municipal system fed from a cistern. Only one pump operates at a time.

We did a follow-up hydrant test, opened three hydrants, one 2-1/2" port at a time until we had six ports open. Pump 3 came on after port 5 was opened and we were flowing more than 2,000 gpm. We flowed 3,250 gpm with 6 ports.

The way I see it, popping sprinkler heads is like opening small hydrants. We needed to open 5 hydrant ports to get Pump 3 into action, providing a large enough opening in the system to allow that much water to flow, and dropping the municipal pressure before the next pump came on.

5x2.5" opening = 5.6" diameter opening, Pump came on

4x2.5" opening = 5.0" diameter opening, Pump didn't come on

30x0.75" opening = 4.1" diameter opening, will pump come on?

Alex

12/20/2021 11:26:38 am

Hi OP,

The third pump will kick on when the flow demand is exceeded by the first two pumps. What was your total flow during your test with all the hydrants? I don't think calculating the equivalent diameter is a fair way to look at this situation.

Alex

12/20/2021 01:26:02 pm

Total flow was 3,246 @ 50 psi residual. Static at 90 psi.

Pump 3 can do it, but it's a matter of ensuring that it comes on.

David Kendrick

12/20/2021 09:58:35 am

Just an outsider's question:

What has been the results of your current flow test?

It might be difficult to ask the municipality to turn on pump three in the event of a sprinkler system activation.

Are there any regulations requiring the municipal water services to provide the demand you are seeking?

12/20/2021 10:18:07 am

Our initial calculations have us looking for 2,353.5 gpm @ 65 psi. With all six ports open, we were able to achieve 3,246 @ 50 psi residual, which meets our requirements. 2677.5 is available at 65 psi, provided pump 3 is operating.

The client serves two major industries in the area, and their ability to serve their two clients keeps a lot of business within the local economy. It is in the municipality's interest that this project succeeds, so they've been cooperative. Just how cooperative they are willing to be is the question. I think that a sensor to activate pump three may be an option.

I haven't come across anything that puts responsibility on the municipality to provide fire flows. I think it would have to be voluntary.

12/21/2021 11:16:15 am

What input are you getting from the customers underwriter?

Having control of the situation with a private tank and pump(s) may be the most reliable solution.

Rely on initial operation of the system through the municipality and have the backup of a pump and tank system.

Certainly more expensive but this would seem to be a underwriter's preference.

12/21/2021 11:29:26 am

The insurer has very few specific requirements - just protect it to satisfy the AHJ. We're in Ontario Canada, and our OBC points to NFPA 13, which in turn points to NFPA 30.

I may not have mentioned that this is an existing building, as well. Not much space for pumps without taking away from income-generating space.

The pump would solve the problem, for sure. At the same time, if at all, the pump would only be required momentarily, until the pump draws down municipal pressure, and that third municipal pump comes on. Full time maintenance for a part-time pump!

Franck

12/20/2021 11:00:02 am

You have to consider the avilable pressure, not only the flow.

Pumps are rated at 100%, but they can provide up to 150% with more than 65% of the nominal pressure.

This being said, when you flow your hydrants, you have a big flow, but maybe 2 pumps can cover the flow demand from your hydrants, with a pressure delivered that is still above the starting pressure of the 3rd pump. This is why it does not start.

Just to give you figures. If your 3 pumps are rated 1000 gpm @ 100 psi, with a churn pressure of 110 psi and an overload point (150% flow) of 80 psi, 2 pumps in operation are able to deliver up to 3000 gpm @ 80 psi. If the starting sequences of your pumps are 100 psi, 93 psi and 86 psi, then you would need more than 2500 gpm demand to start the 3rd pump.

With your example, if the total demand is 2350 gpm @ 65 psi, you have to be sure that your 3rd pump will start at a pressure above 65 psi. If it starts at 60 psi, and 2 pumps are able to provide 2350 gpm at 80 psi, you won't need the third one. And this is not really a problem. It would be a problem if 2 pumps deliver 2350 gpm @ 30 psi and the 3rd pump does not start. In that case, it means that the starting pressure of the 3rd pump is not in adequation with your requirements and you would then need to provide an independent water supply (or ask the municipality to change the setting).

It would be interesting to see what was the flow and residual pressure when you opened 4 outlets.

And as indicated by other peers, you cannot compare 4 x 2.5" opening with 30 x sprinkler openings as this does not consider difference of pipe diamter, pipe length (thus friction losses in the system).

12/20/2021 01:22:21 pm

Only one pump is ever running at a time. First Pump 1, then when it's capacity is exceeded, it shuts off, and the larger Pump 2 turns on, and likewise, when its capacity is exceeded, it shuts off, and the largest Pump 3 comes on.

We get 1700 gpm @ 65 psi with Pump 2 in operation (actual flow was 1980 @ 59 psi residual).

I agree that the opening size comparison is not a reliable method, but I am thinking of this just as an indicator. And as you mention, this does not take into account pipe sizes, lengths, elevations, and associated friction loss, making the anticipated flow/pressure from the sprinklers even lower.

.Mike

12/20/2021 12:00:05 pm

Just a idea, is it possible to have the municipality manually start the 3rd pump for your test?

Casey Milhorn

12/20/2021 03:57:08 pm

Very interesting. So your water supply curve probably looks more like stairs (or 3 different supply curves in one). One ends and the other picks up. Maybe with even better pressure, or maybe less. I guess at the end of the day, as long as you have a hydrant test that proves you have the necessary pressure at system demand, there is no issue. As the system needs more, the pumps appear to operate correctly and provide more. Sounds like your follow up flow test confirms you have the adequate pressure and flow. The only concern might be is if the pressure starts out lower and ramps up, you could have a blind spot in there where a lower system demand (less heads flowing) could have a spot where pressure is too low. To me though, sounds like you have done a great job digging into the water supply and should be in good shape.

12/21/2021 08:12:46 am

That's exactly it - the stepped curve.

And yeah, that blind spot is a concern. Being that the pumps turn off/on at certain pressures, there's also a reliance on the demand that the City is putting on the system at that time. If a fire breaks out during peak hours, then maybe Pump 3 comes on, and everything works as intended. But maybe a fire breaks out at 2 AM, and the pressure doesn't drop enough to activate Pump 3.

So many variables. Lots to think about.

Thanks, everyone for your input. It's been very useful!

Jay

12/20/2021 04:40:52 pm

Perform a hydrant flow test and control the flow from the ports by opening/closing the hydrants, so that you are flowing very close to the 2400 gpm that the design requires. Using the residual pressure from the hydrant during the flow test, calculate the residual pressure that will be available at the base of the sprinkler system riser. If the available pressure exceeds the design demand then the system is good to go, if not then you need to install a fire pump at the base of riser. It doesn't matter how many municipal pumps turn on, only that they turn on consistently and will provide the same pressure/flow points for the life of the building. If the municipality is constantly changing the pressures that the pumps will turn on, then that is an inconsistent/unreliable water supply that you can't design a fire protection system around, and you will need to provide the sprinkler system with its own independent and reliable water supply.

Jack G

12/20/2021 04:52:16 pm

It sounds to me that quite possibly the sizes of the municipal water mains are controlling the flow ( say like in a deluge system— can only flow so much)
Is it possible that municipal system/ mains were installed with only pump # 1, and thru years, as municipal demand increased they added # 2, then #3, without changing main sizes and or routes! You should review their system, May be a lot of 4 and 6 inch water mains.

sean

12/31/2021 06:27:53 pm

have you reached out to the engineering / public works dept.
many with more complicated systems also have simulation information. that info could help you figure out the real world conditions you need to test.

How to Start All Municipal Pumps with Flow Test?

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