Jockey Pump Sizing and Options

Pressure maintenance pumps (PMP), or jockey pumps (JP) as they are more commonly referred to, are an often incorrectly sized part of a fire pump system. Lets walk through the fundamentals.

Why/When Required:

To start with, technically you are not required to provide a jockey pump on all systems.  NFPA 20 section A.4.25 states "Pressure maintenance (jockey or make-up) pumps should be used where it is desirable to maintain a uniform or relatively high pressure on the fire protection system."  The goal is to not shock the system with water hammer when the main fire pump starts. You don't want to be boosting the pressure from 10 psi to 150 psi. You want to be boosting the pressure in the 5-15 psi range.

It is our recommendation that in almost all situations, a jockey pump should be provided to minimize pressure surges when the main fire pump starts.

Jockey Pump Types:

Jockey pumps are not required to be listed per NFPA 20-2010 section 4.25.1.  The failure of a jockey pump results in the main fire pump which would be considered a success.

As such any type of commercial booster pump could be utilized.  However, as a practical matter there are three common types of pumps used.

Regenerative Turbine Pro: Cheap Cost / Low HP Con: High churn pressure - Even the smallest sizes have churn pressures in excess of 400 psi / Must use a pressure relief valve always / Low flow rates - do note expect to fill a large system quickly with these pumps (Anvil Fire does not recommend this type due to ease of accidentally over pressurizing your system)
Vertical Multi-Stage Pro: Very reliable / Can be selected to prevent exceeding system pressure ratings (i.e. 175 psi) / Ease of maintenance Con: Slightly more expensive (Anvil Fire includes this type in all our quotes)
Submersible Multi-Stage If your water supply isn't pressurized (i.e. above-ground tank or city water supply) this is your only option. These are basically "well" pumps and will be submersed down into the water on the end of a 1.25 or 1.5 galvanized pipe.

Sizing of Jockey Pumps

Once you know what type of jockey pump you are using, you need to specify the size/rating. We don't recommend following the commonly referenced rule-of-thumb: a jockey pump at 1% of the rated capacity of the main fire pump.  It does not take into account the volume of your system and anticipated leakages. The sizing of the jockey pump, has very little to do with the size of your fire pump. Lets look at a couple system types and how we would size the jockey pumps.

GPM Rating - Aboveground Only Systems

For situations where the pressure maintenance pump serves only aboveground piping for fire sprinkler and standpipe systems, the pressure maintenance pump should be sized to provide a flow less than a single fire sprinkler. The main fire pump should start during any waterflow situation where a sprinkler has opened, which will not happen if the pressure maintenance pump is too large. 

NFPA 20-2016 section 4.26 states the pump "shall be sized to replenish the fire protection system pressure due to allowable leakage and normal drops in pressure". The appendix language goes on to state "... The main fire pump should start and run (providing a pump running signal) for any waterflow situation where a sprinkler has opened, which will not happen if the pressure maintenance pump is too large. "

One guideline that has been successfully used to size pressure maintenance pumps is to select a pump that will make up the allowable leakage rate in 10 minutes or 1 gpm (3.8 L/min), whichever is larger. From a practical standpoint, jockey pumps are "approximately" rated for 2.5 gpm or 5 gpm. We typically quote our pumps with a 5 gpm rated jockey pump.

GPM Rating - Large Underground Systems

Underground mains are permitted by NFPA 24, Standard for the Installation of Private Fire Service Mains and Their Appurtenances, to have some leakage.  

where:

L = testing allowance (makeup water), in gallons per hour

S = length of pipe tested, feet

D = nominal diameter of the pipe, in inches

P = average test pressure during the hydrostatic test, in pounds per square inch (gauge)

Assuming that you have a system that will not exceed 150 PSI in static pressure, the underground will need to be tested to 200 PSI.

So lets run the following example:

• 500-feet of 6-inch Class 52 Ductile Underground (D = 6.280")
• Hydrostatic test pressure of 200 psi
• Allowable Leakage L = 0.30 gpm

Assuming you have a 2,000 gpm pump, do you really need a jockey pump rated for 20 gpm when the actual leakage should not exceed 0.30 gpm? We are back to our standard practice of a 5 gpm rated jockey pump being adequate unless you have a lot of underground.

PSI Rating - All Systems

Assuming we now know we are going to use a 5 gpm rated pump, what pressure (psi) rating should we select? There are two different design conditions we need to consider:

1. Flow rate to keep up with expected system leakage
2. Maximum expected churn (no-flow) pressure so as to not exceed system rated pressure

Since we know the expected system leakage is generally close to zero, we are mainly concerned with just making sure the jockey pump won't over pressurize the system. There are three different approaches we can take:

1. Adjust controller setpoints so the jockey pump turns off (bad idea for a variety of reasons)
2. Provide a pressure relief valve to accommodate over pressurization (subject to human error and potential mechanical failure)
3. Select a pump with a churn pressure (+ suction pressure) that won't exceed you system rating

Guess what option Anvil Fire recommends? 

Jockey Pump Selection Table Summary

Anvil Fire represents AC Fire / Xylem products and generally follow the sizing chart below for jockey pumps. Reach out to your local regional rep and let us help you narrow down your options.

New AC Fire Fuel Tank Sizes/Design - 2021

Starting immediately, AC Fire is offering a new diesel fuel tank design with more than double the current number of tank sizes available. In addition they will now come standard with emergency vents and a Tnemec N69 Crawford Red paint for better durability. 

Link to PDF literature for new double-wall fuel tank on the AC Fire web-site.

Also check out our blog post on Sizing Diesel Fuel Tanks or the Installation of Diesel Fuel Tanks for Fire Pumps if you want to learn more about the code requirements associated with diesel tanks.

Please reach out if you need additional information.

 

Fire Pump Rating (Size) Selection

Fire pump sizing is not like commercial pump sizing. We don't care about efficiency, and you order pumps in only specific sizes. This article touches upon some items to consider when picking a fire pump.

In general, the first step is determining your system demand point. Discussion of how exactly you determine this is beyond the scope of this article and has a lot of nuance depending upon your site-specific needs. However, for simplicity let's assume that you have a dry-system in an attic with a demand point of 305 gpm (2535 sq ft x 0.10 gpm/sq ft x 1.20 overflow/imbalance factor).

Rated Flow (gpm) Sizing

The first item you must specify is the pump flow rate. Per NFPA 20 (2013 edition) table 4.8.2 pumps are only allowed to be listed with the following flow rates in gpm:

• 25, 50, 100, 150, 200, 250, 300, 400, 450, 500, 750, 1000, 1250, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000

So with our example demand of 305 gpm, would you go with a 300 or 400 gpm rated fire pump?

While manufacturer's pump curves go way beyond the ratings above, NFPA 20 section 4.8.1 only allows you to use a fire pump out to 150% of its rated capacity. That means that a 300 gpm pump can be run out to 400 gpm (300 x 1.5) and could easily meet the example demand flow rate. One could even use a 250 gpm pump with the corresponding max flow rate of 375 gpm (see the bottom of this article for additional discussion).

The other common condition is a standpipe. Assume you have two stair-towers and total demand of 750 gpm. Should you run a 500 gpm out 150% to 750 gpm? In our opinion that is probably a poor choice since you are so close to the 150% limitation.

So what is the harm in just selecting the next pump size up (i.e. 400 gpm for our 305 gpm example demand)? First, can you water supply handle flowing at least the 100% and/or 150% flow rate? While technically NFPA 20 allows you complete testing at less than 150%, if you can avoid this situation it would be better.

Second, there may be some hidden cost. For example going from a 400 to 500 gpm pump also means you go from 4-inch suction to 6-inch suction (see our NFPA 20 pump pipe size look-up app at https://anvil-fire.com/apps_pump_sizing.html). In addition, you are generally probably increasing the horsepower and therefore the overall cost of the equipment. Or even causing an electrical transformer to be upgraded.

Note that FM Global only allows you to run the pump out to 140% of rated pressure.

Rated Pressure (psi) Sizing

The second item you must specify is the rated pressure you want. Manufacturers must list each pressure rating in order to maintain listing with UL and FM Global. On occasion you will find some holes in approved pressure ratings, but AC Fire has a long history and therefore an amazingly wide range of rated pumps to accommodate almost any demand.

While not directly impacting your selection, it should be noted that NFPA limits manufacturers to how "steep" their curves can be in regard to pressure. See the curve below for the specifics. These limitations are a non-issue when you buy a listed pump as they have already had to comply with the limitations.

However, you should pay careful attention to the churn pressure (sometimes also called shut-off or dead-head pressure). When a fire pump is not flowing any water it produces the highest discharge pressure. In general most fire sprinkler components are listed to 175 psi.

Let's take the example of you have 50 psi static pressure from the city + our 100 psi rated pressure for a total 150 psi when flowing the 100% rated gpm. Sounds good, right? Maybe not if your churn pressure is 126 psi which is not unthinkable depending upon the specific pump selection (50 psi static + 126 psi churn = 176 psi). Always provide the max city pressure to your pump rep and look at the pump specific curve to ensure no surprises in the field.

In addition, make sure you check how much pressure you have at your desired flow rate from the city water supply. You can use the formula below or just use the quick calculator at https://anvil-fire.com/apps_log_graph.html

      

Check out AC Fire's online pump selector at https://www.selectacfirepump.com/ and play around with some selections, or reach out to us at sales@anvil-fire.com for support on your projects in the NorthWest.

A quick reference chart for the 150% and 140% flows of the various pump ratings.

Rated Capacity	150%	140%
25	37.5	35.0
50	75	70
100	150	140
150	225	210
200	300	280
250	375	350
300	450	420
400	600	560
450	675	630
500	750	700
750	1,125	1,050
1,000	1,500	1,400
1,250	1,875	1,750
1,500	2,250	2,100
2,000	3,000	2,800
2,500	3,750	3,500
3,000	4,500	4,200
3,500	5,250	4,900
4,000	6,000	5,600
4,500	6,750	6,300
5,000	7,500	7,000

Diesel Exhaust Requirements

The exhaust from a diesel engine driving a fire pump is an often-overlooked item.  The high heat put out by the exhaust is a hazard to occupants and can greatly contribute to overheating the room itself. NFPA 20 (2013 edition), section 11.5 covers "Engine Exhaust" and should be carefully reviewed. However as a starting point, the following items should be considered.

Exhaust Discharge Location

The first step is to determine where you are going to discharge the exhaust gases. NFPA 20 section 11.5.3 for "exhaust discharge location" has the generic common-sense requirements of do not discharge where you might hurt people, damage the building, or directed on combustible materials. But very little specific requirements are provided. There is a loose reference in NFPA 20 back to NFPA 37 (Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines). In addition, the International Mechanical Code (IMC) section 915.1 directs us back to NFPA 37 for guidance.

NFPA 37-2018 edition section 8.2.3.1 has the same generic recommendation that "Exhaust systems shall terminate outside the structure at a point where hot gases, sparks, or products of combustion will discharge to a safe location."

Not well referenced by the codes around exhaust, are the requirements for intake louvers.  These requirements provide more hard numbers that the exhaust sections.  The IMC section 401.4 requires intake louvers to be a minimum of 10-feet away from any hazardous or noxious sources (diesel exhaust would be considered noxious).

Example Exterior Exhaust Discharge - Not near any doors

Exhaust Sizing

Don't assume that just because the engine and muffler have a 4-inch connection, that you should run 4-inch all the way to the exterior.  Back-pressure on the engine due to excessive distances to the end of the exhaust pipe can cause poor engine performance. NFPA 20 states that the exhaust shall not be smaller than the engine outlet size and be as short as possible. NFPA 20 section A.11.5.2 further provides the generic guidance that if you have more than 15 linear feet (4.5 meter) of exhaust pipe, you should increase your exhaust one pipe size for each additional 5-feet (1.5 meters) of length.

However, rather than using this generic rule-of-thumb, we recommend consulting with the manufacturer.  Both Clarke and Cummins have some very easy to use calculators so that there is no question about exhaust sizing. Links to their web pages are provided below:

• Clarke Fire Exhaust Back-Pressure Calculator

• Cummins Fire Power Exhaust Back-Pressure Calculator

Exhaust Through Walls/Roofs

Obviously you don't want to put your 1200 F degree metal exhaust against wood studs and siding. NFPA 20-2013 section 11.5 provides the following guidance:

• COMBUSTIBLE ROOF - Guarded at the point of passage through the combustible roof by ventilated metal thimbles that extend not less than 9-inches on each side (above and below) of roof construction and are at least 6-inch in diameter larger than the exhaust pipe or duct.

• COMBUSTIBLE WALL - Metal ventilated thimble not less than 12-inches larger in diameter than the exhaust.

NFPA 37-2018 section 8.3 is also applicable for exhaust gas temperatures less than 1,400F (760C). Based upon a quick review of the data sheets for Clarke and Cummins, the typical exhaust temperature does not exceed 1,100 F. The requirements of NFPA 37 are basically the same as NFPA 20.

Diesel Exhaust Wall Thimble - Exterior

Diesel Exhaust Wall Thimble - Interior

Insulation

The exhaust pipe shall be covered with high temperature insulation or otherwise guarded to protect personnel from injury. This should also include the required minimum 12-inch flexible piece shall be installed between the engine and the exhaust piping (this piece is provided standard with all packages provided by Anvil Fire).

Diesel Engine Exhaust - Without Insulation

Diesel Engine Exhaust - With Insulation

Contact Anvil Fire (sales@anvil-fire.com) for support and sales of any product referenced in this article.

UL 448 - Fire Pump Horse Power Changes

Effective November 1, 2019, Underwriters’ Laboratories (UL) Standard 448 has been revised to change the maximum horsepower required by the driver (electric motor or diesel engine) paired with a fire pump. The new requirement specifies that maximum brake-horsepower must be demonstrated during each performance test. If the maximum horsepower developed is greater than current motor or engine horsepower offering, the pump will fail testing under the new criteria. This is an industry-wide change, meaning compliance is required by all UL listed fire pump manufacturers.

To maintain compliance with the Standard, driver requirements for numerous fire pumps have changed for all manufacturers with any orders shipped beginning November 1, 2019.

Vertical turbine fire pumps, by the nature of their design, are not affected by the change in Standard.

The UL448 Standard pertains only to centrifugal pumps, therefore positive displacement pumps, are not affected by this change. 

FAQs

Does this change in the UL448 Standard affect both electric-driven and diesel-driven fire pump packages? Yes, this change applies to both electric and diesel fire pump packages.

You state “maximum brake-horsepower must be demonstrated during each performance test.” Haven’t fire pumps always been tested this way? Until now, fire pumps have been tested up to shortly beyond the secondary duty point (i.e. 150%) and not to runout (can be up to 400% of the pump rated flow)

What about replacement pumps? Might they need higher horsepower drivers or are they “grandfathered” in? All fire pumps shipped after November 1, 2019 must be compliant with the new UL448 Standard, meaning some horsepower requirements may increase. This applies to replacement pumps, as well as pumps for new installations since they all must undergo Certified Performance testing and demonstrate the maximum brake horsepower during this test. Rotating elements can be replaced like-for-like.

New FM Global Fire Pump Marking Requirements

FM Global is updating their nameplate requirements for fire pumps. Nameplates for pumps manufactured after October 1, 2017 must now include the name of the pump driver and pump controller manufacturers and serial numbers per the sample below:

"With the global expansion of our business, we have seen a dramatic increase in the number of FM Approved fire pumps and pump packages worldwide," notes Dave Fuller, manager of FM Approvals' fire protection group. "This means that more and more manufacturers must rely on multiple facilities for distribution and shipping, and with that have come additional challenges to ensuring complete FM Approved pump packages are being supplied. By requiring more details be included on the pump or pump package label, we are increasing the transparency of this requirement to the end user. This creates a stronger paper trail and easier verification, and will help all parties involved should there ever be a question about a specific fire pump package."

Anvil Fire has seen instances of other distributors assembling different manufacturers together in their shop to save money. However, FM Global has always required that the serial number of the pump and controllers to be recorded at the factory. It is clear that FM Global is trying to further enforce this requirement.

Visit the FM Global web-page for additional information: http://www.fmapprovals.com/product-alerts-and-news-events/approved-product-news/approved-product-news-recent-issues/2017/apn-volume-33-issue-1/fire-pump

Diesel Engine Cooling Loops

Make sure you are in compliance with FM Global's requirements for cooling loops on diesel engines. FM Global Approval Standard 1333 was updated in 30 Nov 2013, but compliance was not required until 1 April 2015.

Clarke Fire has an excellent write-up on their web page that you can find here. But, we wanted to summarize the key requirements.

• FM Approval - Cooling loops are now required to be approved and therefore they will have the FM logo on a nameplate.

• Low Raw Water Flow Alarm - This switch is set to activate at 75% of the required flow rate.

• High Raw Water Temperature Alarm - This switch is set at 105F (40C).