Listed Approach to Prime Fire Pump w/ Seawater?

1/24/2022

We have an external fire protection network in a marine port that has been served by 2 main electrical-driven fire pumps.

The proposed solution on this project is to utilize two main end-suction-type fire pumps using the seawater as a water supply source.

The seawater is near the seashore at a lower elevation than the fire pump base.

To overcome the low pressure of the Net Positive Suction Head, a vacuum priming pump is installed on the suction line to get enough pressure to prime the fire pumps.

Considering this whole assembly is not listed nor approved, and there is no space for a water storage tank, what feedback might you have about the non-listed solution?

We can't provide an extended platform here with a vertical shaft turbine pump, so I'm at a loss for solutions. Thanks in advance.

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12 Comments

Steve Frederick

1/24/2022 08:13:29 am

At the risk of providing a grossly oversimplified answer, why not use a backhoe to dig a channel from the shoreline to a vertical turbine in the pump house on the shore, and bring the sea water to the pump, as opposed to bringing the pump to the sea water?

Franck

1/24/2022 08:15:53 am

Priming tanks are still used in Europe where horizontal fire pumps are still allowed to take suction under lift.
I am not a big fan of such installations as you may have some reliability issues.

For the little history, earlier editions of NFPA 20 allowed centrifugal pumps to operate under suction lift, when they were provided with tank of priming water. After several foot valve failures that caused the loss of the priming water that destroyed the pumps running them dry, they were outlawed by NFPA 20 standard, beginning with 1974 Edition.
You may find some information if you have access to these earlier editions.

Here are some tips (this will not fulfill the NFPA requirements, but help to limit possible issues):

The maximum depth from which the pump would suck should not exceed 3.2 m (10 ft 6 in.).
In practice, the pump should be installed at the nearest position to the suction location.
Independent suction pipes should be provided where more than one pump is supplied under lift from the same intake or suction well.

The size of the suction pipe should be such so that with all pumps operating at overload capacity (150%), the total operating suction lift will not exceed 4.6 m (15 ft).

The suction pipe should be immersed in water with an elbow, and a filter flap (or foot valve) should be installed to the suction pipe end side to keep water between the water level in the tank/pond/river and the pump casing.

There is no need to install a shut-off valve onto the suction line. The filter at the suction flap end should be occasionally cleaned up and prevented to be clogged with dirt and foreign substances.
During cleaning, this process should be conducted by removing the suction pipe without emptying the reserve tank.

A priming tank should be installed, to avoid that air is present in the casing instead of water.
The priming equipment should have sufficient capacity to displace the air from the pump and suction pipe within 3 minutes.

Franck

1/24/2022 08:17:28 am

And some information regarding the prriming tank itself:

The installation should be done in accordance with the following:
- A priming tank should be provided to fill the volume between the backflow preventer and the foot valve (upstream and downstream).
- Only one pump should be supplied per priming tank
- The bottom of the priming tank should be at least 1.5 m (5 ft) above the top of the pump
- Automatically filled tank only are accepted: volume at least 500 l (130 gal.) or 3 times the volume of the suction pipe + pump casing, whichever is the greater
- If a manually filled priming tank is provided anyway, the minimum volume should be at least 950 l (250 gal.) or 3 times the volume of the suction pipe + pump casing, whichever is the greater. Replacement with an automatic filled priming tank is then advised.
- The water supply to the priming tank should be capable of keeping the tank full at all times.
- The priming tank should be connected to the pump discharge upstream of the check-valve, with minimum DN 50 (2 in.) diameter pipe. The connecting point should ensure that all priming water enters the pump and suction side, and is not wasted in the discharge pipe of the pump.
- The priming connection should be fitted with a gate valve and a check-valve, as close as possible to the pump
- The priming tank should be fitted with a low level gauge, set at 2/3 of tank volume, to automatically start the pump on a low level condition, and allowing tank refill through a calibrated orifice

Shady

1/24/2022 01:12:56 pm

Your explanation is very clear enough but if you have a diagram or draft for this assembly it will be very fruitful.

Franck

1/24/2022 03:17:18 pm

Contact me @ [email protected]

Franck

1/24/2022 08:21:50 am

Note that in your case, you have the additional issue of using salt water.
You may use the good advices formluated in NFPA for water supplies provided in marine applications.

In particular, it could be a good practice to use an additional pressure tank.
• The tank should be filled with freshwater
• The size should be calculated for:
The flow requirement of the hydraulically most remote system demand for 1 minute for wet systems
The flow requirement of the hydraulically most remote system demand for 1 minute plus the volume to fill all dry piping for preaction, deluge and dry pipe systems

1/24/2022 08:32:38 am

At the risk of seeming stupid, (and having never been near the coastline), wouldn't sea water cause a lot of corrosion in the pipes?

Glenn Berger

1/24/2022 08:43:19 am

Stainless steel (good grade) is typically utilized for this application.

Franck

1/24/2022 11:27:22 am

In addition to marine applications (where salt water is used for some obvious reasons), it is quite common to find such installations for large plants on the Coast.

The water supply is generally limited to hydrants and hoses (with a dedicated fresh water supply for sprinklers), but sometimes also for sprinklers.

But not a real desirable situation because of the corrosion issue + possible salt and other deposits accumulation at some areas that could block the sprinkler orifice, preventing a proper water distribution pattern.

This requires much more maintenance and the maintenance cost, over the years, may overpass the cost for the provision of a dedicated freshwater tank supply.

Glenn Berger

1/24/2022 08:44:29 am

Overall - work with the AHJ on this custom design configuration.

Jesse

1/24/2022 08:47:22 am

I don't envy your position, and there is a lot that can go wrong. I think Franck covered all of the bases. Its not a perfect answer, but I don't think there is one to your situation.

Franck

1/24/2022 11:20:38 am

You're fully right
The solution can't be NFPA compliant and the final reliability would remain questionable, especially on the long term.

I really don't like horizontal pumps taking suction under lift when I found one during one of my inspections.
There is always an issue (leaking foot valve, issues with the priming tank...).

But this configuration is still allowed in some European places... and not unusual.

Listed Approach to Prime Fire Pump w/ Seawater?

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