Well pump & pressure tank for fire hall
Well pump & pressure tank for fire hall
(OP)
I am helping to design the plumbing systems for a new municipal building in Eastern Canada (New Brunswick) that will house a volunteer Fire Department and the municipal offices. The Fire Department requires roughly 200GPM of water flow from the well in order to fill their trucks. The building includes washrooms, showers, janitor closet and a kitchenette. The building is occupied by a max of two persons, Monday-Friday, 8-5. The building may be used for other activities on weeknights. We are concerned about sizing the pressure tank for the domestic water system based on the pump, which is 20HP. That would be a very large pressure tank. The reason for this is we are worried that with so little demand on a typical day (assume 16 gals a day max), it will take quite a long time for the pressure tank to deplete and the pump to kick in. We don't want stagnant water. We want to specify a VFD well pump with an 80 gal pressure tank. I am looking for suggestions on how to design this or opinions on our preliminary design.
thank you very much
thank you very much





RE: Well pump & pressure tank for fire hall
Even if turned down to 100 gpm will get you only 1/4 of the way up to the surface.
The VFD turned down to 20 gpm will hardly get the water out of the pump.
Use the well pump only to fill the fire truck tanks.
Get a small separate water tank and have a commercial water service truck bring potable water once a month.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
A storage tank makes sense with a level control system to keep the tank filled for the domestic service, float isolating valve to shut off the storage tank when the tankers are being filled, connect a small domestic pressure pump / system to the storage tank for domestic service.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
When I worked for the water well industry, we visited a guy in Oregon that made an apparatus so that you could put two pumps in a well; One on top of the other.
let me know if you want information on something like this. If it's a one time thing, I remember enough about it to explain the design. It was easy enough to manufacture.
Charlie
www.facsco.com
RE: Well pump & pressure tank for fire hall
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Well pump & pressure tank for fire hall
How long do you envisage that it will take the water to become stagnant - and is the water from the well drinkable anyway?
Have you considered of a deep well ejector pump surface mounted with a pressure tank. The drive pipe and return pipe require very little space in a well casing. Should be available off the shelf from a number of supplier.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
We've gone full circle.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
- The storage tank would not actually be "open to atmosphere"; just a standard water storage tank, same as a cistern. It would be fairly small, say 80 gals. This would eliminate our worry for freshness of water for domestic purposes.
- A separate well is still our worst case scenario option. We were given a quote of roughly $9,500 for the well and pump.
- Regarding the idea of two pumps in the well, the well driller told us it would be very difficult and did not recommend it. He was concerned over having to remove the top pump in order to service the bottom pump. The well casing is 8", the fire department line is 4" and the domestic water system requires 1-1/2" to 2" max. The well is 200 feet deep with the casing down to 130 feet.
FACS: if you could forward me that information, that would be great!
- Yes the well water is drinkable; further to this, we are specifying carbon filters at the faucets.
- TenPenny: I agree with what you are suggesting, but the large capacity of the pump required for the fire hall vs the small pressure tank is what is concerning us at this point. Essentially, even with a soft start drive on the 20 HP pump, it will only take 30 seconds - 45 seconds for the pump to fill the 80 gal tank. Based on our calculations, this would happen 2-3 times a week, so we aren't terribly concerned about short cycling the pump. Just trying to get a feel for how this surge will affect the system in whole.
- jonr12: How would the constant pressure valve protect the domestic system from the surge of water from the 20HP pump? I assume the valve would release when pressure of 60-70psi is reached?
- We are also considering a small expansion tank to help with water hammer.
RE: Well pump & pressure tank for fire hall
The storage tank needs to be sized appropriately considering what capacity you need to fill the trucks, and at what rate you can refill this tank.
Out of curiousity, where in NB is this located?
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
If you pump from the well to a booster tank, Potable water will be renewed every time a truck is filled.
If there is enough space, you can pump from the well to an elevated tank, and fill the trucks by gravity. This way you will save a pump.
If the elevated tank is big enough, you even can use an smaller well pump. (But will be pumping more time).
RE: Well pump & pressure tank for fire hall
The aquarium in my living room has half a month's supply.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
No need for any above ground tank with water available on-demand for your building.
Link below describes the operation etc of a deep-well jet pump - costs probably a few hundred's, easy to install and maintain.
http://inspectapedia.com/water/JetPumps2Line.htm
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
The issue I see is that he needs to have fresh water for potable use, and a reservoir tank for filling the trucks. You could do this with one pump, all you have to do is separate the plumbing above the well head, so that the potable water comes directly from the well. Why not just use check valves, so that the pump kicks on when there is demand either from the potable side or the truck supply side, but that neither downstream use will cross feed the other? I don't see why two pumps are needed.
RE: Well pump & pressure tank for fire hall
To use the well pump for the building supply is over-kill, open a tap for a drink of water and you bring a 20HP pump on-line for 5 - 10 seconds.
I see only one reasonable solution, the well pump dedicated to filling the tanker, and a seperate deep well pump with pressure tank to service the building.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
Anyway seems the OP has given up.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
- Yes, the well can provide 200 gpm. Well is 300' deep.
- We are looking into the deep well pump option. Do I understand correctly that a submersible pump could be installed in the well in conjunction with a deep well pump? We are back to two pumps on a single well; other than capital cost, what are the cons to this setup?
- We can't count on potable water being replenished when the trucks are filled; the fire department does not get that many calls.
- Trucks are 1250 gals (2), 2800 gals (1) and a future 4000 gals tanker (1). The client wishes to have capacity to fill one 2800 gal truck at this well.
- What is the advantage of using a storage tank for the truck fill? Why not pump directly from the well?
- Here is our current design, comments are appreciated:
20 HP submersible pump to 4" line into building, 4" line ran directly to fire truck fill stations, 1-1/2" line tee-ed off from 4" main to 80 gal pressure tank for domestic use, control valve located on 1-1/2" line prior to pressure tank. Pump complete with soft start drive. Pump rep is not concerned about burning out the pump, as it will only turn on every few days to replenish the pressure tank. For the amount of time is will run for domestic use, we are not overly concerned about operating costs either.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
A constant pressure valve or CPV will start and stop the pump at 5 GPM, no water hammer at all. 80 gallon diaphragm tank holds 20 gallons of water. The CPV is set at 50 PSI with a 40/60 pressure switch attached to the tank. When using water domestically, the CPV makes the pump work like a 5 GPM pump. It starts and stops the pump at 5 GPM, and refills the tank at 5 GPM, which takes about 2 minutes at those pressure settings. Not very efficient to run a 300 GPM pump at 5 GPM, but you only use 16 gallons per day, so who cares. Because the amps are reduced the motor gets plenty of cooling at 5 GPM, and won’t be damaged. When you need to fill a truck, the CPV will open up and supply as much water as the pump can produce while holding 50 PSI. In this way one pump can do both jobs.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
Starts and stops of the pump are the worst duty cycle possible.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
A 4-Inch well pipe has a water capacity of 0.65 gals/ft. If you use 16 gals per day, it will take 2 weeks for the water to move through the well pipe, and an addtional week or so to go through the pressure tank. If you consider that the office is probably closed on weekends, you have one month of travel time for the water in the system from the bottom of the well to the tap. One would think that would meet the definition of stale water.
Using a single pump for both applications may be the cheapest solution, but it is not the best solution. If you are going to all of the trouble to build a new municipal building, why chintz out for just a few thousand on the water supply. Remember the phrase, "The pain of poor quality lasts far longer than the joy of a low price".
jonr12:
Where do you come up with this concept:
"I have also found that starting a pump against a closed valve will make the motor start under a no load condition, which reduces the starting current equal to or even less than a soft start panel."
That is not correct.
In actual practice, submersible well pumps actually have 4:1 starting current:operating current ratio (instead of the typical electrical pump motor's 6:1 ratio) because of the small diameter of the pump impeller (as compared to a centrifugal pump). That is the reason that soft starts are not typically used on submersible well pumps.
RE: Well pump & pressure tank for fire hall
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
Just in case the OP missed my earlier suggestion, simplest method for a good permanent easy to operate / maintain installation is a down-the-well 2 pipe jet pump with above ground diaphram pressure tank pump, seems the well casing is 8" (OP comment) so should be enough room for the jet pump and the riser pipe from the pump.
http://inspectapedia.com/water/JetPumps2Line.htm shows a typical arrangement.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Well pump & pressure tank for fire hall
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
A 4-Inch well pipe holds .65 gals of water per foot of length. The OP says that the well is 300 feet deep. That means he will have 195 gals sitting in the well pipe. What is arbitrary about that?
On another tack, perhaps the OP has underestimated the water usage. We would generally use 15 gpd per employee. With the 2 employees, that equates to 30 gpd.
http://www.ilga.gov/commission/jcar/admincode/035/...
In support of a higher estimated water demand, the OP has also stated "The building includes washrooms, showers, janitor closet and a kitchenette."
A modern building would also include a 1 to 1.5-Inch water service as well.
RE: Well pump & pressure tank for fire hall
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Well pump & pressure tank for fire hall
This is true. Starting a submersible with an open discharge line will usually causes the starting amps to be about 6 times the running amps. But have you ever checked the starting amps of a submersible motor with no pump attached? The starting amps peak is only 1 to 2 times the running amps. It is the same with centrifugal pumps and motors. I learned this using one of those magnetic couplings between the pump and motor. With no load on the motor, the starting amps are not any higher than with a soft start panel.
So when the system is pressured up and the pump starts against a closed valve, the starting amps are the same as if the motor was started without a pump attached. The only time you see the 6 times running amps is the very first time the pump is started when the pipe is empty and there is no pressure to hold the valve closed. After the first start and the system is pressured up, the starting current is the same or even less than when using a soft start panel.
It is just as important for the pump to get exercised as it is for the water to stay fresh. You want to make sure the pump hasn’t rusted up and locked down, so it will work when you have a fire. So it would be a good thing for the pump to start and run a couple of minutes everyday to keep it in ready condition. Then if you want the water to stay fresh, just use a little more than 16gpd. Maybe hook up a sprinkler with a timer and water the grass for a few minute every couple of days.
RE: Well pump & pressure tank for fire hall
The reason no soft start is required for a submersible pump is that the rotational inertia of the pump is low. The impeller diameter is much smaller than the common centrifugal pump impeller. That is why the well pump starting amps are 4:1 ratio of operating amps. As a result of the low inertia design, the pump starting time is also low, less than a second.
Submersible well pumps are also always designed to drain back into the well on pump shutdown so that you are not restarting against a full water column. In summary, for a submersible well pump, it does not make any difference if you are starting against a closed valve or open valve. The submersible well pump is designed to start against an empty column pipe.
DomDoucet: The fire water system design should be reviewed by a fire protection specialist with experience in rural fire systems. There may be additional requirements such as an automatic stand-by generator, or at minimum, an ability should be provided to rapidly connect a mobile generator in the event of a long term power failure. There may be minimum insurance requirements such as FM approval of components. Specific requirements and technical details should be based on fire department and health department requirements and local engineering standards.
RE: Well pump & pressure tank for fire hall
When using a soft starter and starting a pump against a closed valve, you have to turn the torque setting way down. Otherwise the starting load on the pump/motor is so low that it will go to full speed almost instantly, no matter how long you have the soft starter set to ramp up.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
I constructed a 1000-feet deep well recently. Are you stating that you would try to start a well pump against 1000-ft of head?
That is exactly the reason that the check valves are allowed to leak water back down into the well. It is a fact that the check valves allowed the water to drain back into the well. It is also a fact that there was no soft start. It is also a fact that the well pump does not start against a closed valve. Reread the other details above.
RE: Well pump & pressure tank for fire hall
Yes I would rather see the pump start against 1000’ of head than with no head. I have done some that where twice that depth, and I would never let them drain back. The deeper the well, the harder it is for the pump to start when the pipe is empty.
RE: Well pump & pressure tank for fire hall
If the well pipe is empty, the pump will have to run that much longer to fill the discharge pump and start working against the higher head.
Not explained particularly well, but I'd much prefer having a check valve.
RE: Well pump & pressure tank for fire hall
The driven load type / inertial will have effect on the starting time.
Starting a centrifugal pump with closed valve or static head will take shorter time than starting with a open valve or zero/low static head.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
The driven load does have a lot to do with starting current. The starting current for a motor with no pump attached or pumping against a closed valve is only about the same as the running current. With a pump attached and starting at zero head the current can be six times the running current.
RE: Well pump & pressure tank for fire hall
Check out a current / speed/ torque curve of a motor. It has no relationship to the driven load. The starting current is expressed as xxx% of the full load current. Not the operating current. Operating current depends on the load.
RE: Well pump & pressure tank for fire hall
http://books.google.ru/books?id=GjpZFOQeH3cC&p...
"Starting a pump against a closed valve is only recommended for pumps with low specific speed, where the power input and speed is less than the pump duty point."
"Starting the centrifugal pump with a shut discharge valve is standard practice with many operation departments. The concern is to save power without realizing the damage that is being done to the mechanical seal, impeller, wear rings and bearings. "
http://www.mcnallyinstitute.com/06-html/6-7.html
RE: Well pump & pressure tank for fire hall
http://www.rmhindustries.com/wp-content/uploads/20...
This shows when the motor is disconnected from the load there is about 15% less peak load at start up and a big difference in time. I find submersibles to do much better. I guess that is because of what bimr says and I quote here.
“Submersible well pumps have slightly different operating characteristics than the common centrifugal pumps. The reason no soft start is required for a submersible pump is that the rotational inertia of the pump is low. The impeller diameter is much smaller than the common centrifugal pump impeller. That is why the well pump starting amps are 4:1 ratio of operating amps. As a result of the low inertia design, the pump starting time is also low, less than a second.” bimr
My peak amp meter shows a submersible starting when the pipe is empty to be almost 6 times the running amps. I believe my meter is correct because this is the same as it says in the motor specs from Franklin between SFA and Locked Rotor Amps. But when starting with the pipe full and against a closed valve I only see about 2 times the running amps. This is about the same as I see when ramping up with a soft starter. My amp meter is telling me that starting against a closed valve greatly reduces the amp draw, and I have yet to see any of the failures mentioned for doing so. I have tried different meters and they all say the same thing. So you are right, I am confused, because I believe my meter.
RE: Well pump & pressure tank for fire hall
"A. Starting Centrifugal. The almost closed discharge valve creates a minimum load on the driver when the pump is started. ... Assuming that the motor inrush current allows and that the motor will not kick off, the discharge valve may be just "cracked" — about 1/8 open — before the pump is started."
http://books.google.ru/books?id=cHI17qlMXpwC&p...
There is a difference between a closed valve and an "almost closed", "cracked" or "throttled" valve.
One final comment is that I have been referencing large pumps (450 HP} where you are referencing small HP pump. Most likely the motor characteristics are slightly different.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
The starting current is a tricky subject. With the fast start, it is not an easy measurement to take. For the briefest fraction of a second locked rotor amps is seen until the rotor actually starts turning. It then decreases as the motor speeds up until it reaches the operating speed, at which the current should be steady. A soft starter lengthens the time it takes to get from the initial start to operating speed, thus reducing the amperage draw at any moment of the start, but with the converse of actually generating more heat from the motor over the length of the start (but not enough to make a difference if the motor has water flowing past it, i.e. not against a closed valve).
RE: Well pump & pressure tank for fire hall
This is also evident in the fact that the motor must stay off for a minimum of one minute, to allow the internal motor heat to dissipate. It takes the same minute of time for the heat to be transferred to the motor housing after starting a cool motor.
The following is a letter from Sun Star, who is the Hitachi motor company in the US, which is also the same motor as Centri-pro from Goulds and Pentek from Pentair or Sta-Rite. It seems that if the motor is de-rated enough, (pulling reduced amps), that it will even function properly with no flow past the motor.
Dear Customer
All submersible motors require cooling flow past the motor to dissipate heat generated within the motor. Hitachi has a standard for ambient temperature and required flow dependent on load. And although the specifications of your application are not covered on this chart we have performed extensive testing covering ranges outside the chart.
In your application (5 GPM, 7" shroud, 6" motor with an actual O.D. of 5.5") the flow velocity past the motor will be .109 feet per second. At this flow velocity at an ambient temperature of 95°F the service factor of the of the motor will be .82 and the motor must be de-rated from 10 HP to 8.2 HP with no service factor. Your application of 6 HP at 60-77°F at this same flow is well within the allowable limits of the motor rating at this reduced flow and temperature. We would expect lower internal motor temperatures, which will actually increase your service factor in this operating temperature range (60-77°F). We have performed research at temperatures above and below 77°F with "No-Flow" and the motor has performed satisfactorily. We anticipate no problem with your operating range.
Thanks you for this opportunity to be of service. If you have any questions or desire additional information, please do not hesitate to contact this office.
Sincerely,
Kevin P. Price
Vice President Sales & Service
Sun-Star Electric, Inc.
RE: Well pump & pressure tank for fire hall
The motor will start from dead stop to full speed in a time period of approximately half a second. Any benefit of throttling the valve on startup for the time period of half second will be slight. However, the downside of throttling the valve longer than the half second startup will be probably be much greater than any possible benefit.
At best this seems to be an academic exercise as nobody will be interested in absorbing the costs to throttle a valve for such a small motor.
RE: Well pump & pressure tank for fire hall
The cool down period is actually 15 minutes between shutdown and restart (check the Installation and Operation manual that comes with the motor). This is because the cooling of the motor is reduced when the water around it is not flowing and the heat generated at startup is added to any existing heat in the motor. Many motors are killed by ignoring this simple rule. The motor does not take a full minute for the heat to get to the motor housing. The flow past the motor keeps the external temperature of the motor down, which aids in the heat transfer process. You may only measure a 10°C rise of the motor externally, but the internal temperature is much higher.
The letter you reference is for a specific motor in a specific instance. The information is only really applicable to certain motors in certain circumstances. You are referencing a small 2 Pole, 6” Hitachi motor. The construction of a 6” Hitachi is different than any of their other motor sizes. The heat handling capability of the 6” motors depends on the horsepower. What works for a 10 Hp does not necessarily apply to a 25 Hp. The motor used was probably one of their Hi-Temp motors, which but rated for more than double the ambient temperature of their standard motor. Heck, I am surprised they did not just reduce the size of the shroud to get a higher flow rate and avoid the problem completely.
To de-rate a motor so you can run it at a no flow condition makes no sense. You would have to buy a larger motor (probably much larger) and then run it at a lower load point, where the motor efficiency is much poorer, thus increasing the cost to run the motor. It would be much more cost effective to operate the motor properly, with the correct flow, than to force a no flow condition on the motor (which would probably reduce the life of the motor). Heck, it would be cheaper to have a motor custom built to handle the conditions than to operate a motor that far from its load rating.
RE: Well pump & pressure tank for fire hall
The OP is asking about a 20 HP, 6”, 2 pole motor. Below is another letter from Sun Star being ask about a 30 HP motor. This 30 HP motor is being de-rated to a 15 HP load by simply restricting the flow. You don’t need to put on a larger motor to de-rate, simply restricting the flow with a valve will do that. The letter states that a 30 HP motor only needs to be de-rated to a 24.6 HP load to work safely at 5 GPM flow. This particular 30 HP will drop to a 15 HP load when restricted to 5 GPM flow, which is de-rated even more, and requires even less flow for cooling. These are standard motors, no special high temp design.
Operating a pump at 200 GPM all the time would take a very large pressure tank. Then at 16 gpd use, the water in this tank will be sitting idle for many days getting contaminated. It would be much better to fill a small pressure tank at reduced flow, as long as the amps decrease (de-rating the motor). Starting against an almost closed valve or running at reduced flow with reduced amperage will not hurt this pump or motor.
You can’t reduce the size of the shroud without starving the pump at high flow rates. Throttling with a valve will be much less expensive than a large pressure tank or any other way to do this job. The inefficiency of running a 20 HP motor that is pulling about a 12 HP load while pumping 5 GPM for only a couple of minutes per day doesn’t add up to much. The effect of exercising the pump/motor every day or two and not having a lot of stored water to worry about more than makes up for any inefficiency. After all, one of the most important things is that the pump will be in working condition and able to supply 200 GPM when needed for an occasional fire. Letting it sit idle for days or weeks at the time may mean that the pump will not start when there is a fire and it is really needed.
Dear Customer
In your application (5 GPM, 7" shroud, 6" motor with an actual O.D. of 5.5") the flow velocity past the 30 HP motor will be .109 feet per second. At this flow velocity at an ambient temperature of 95°F the service factor of the motor will be .82 and the motor must be de-rated to 24.6 HP with no service factor. Your application of 15 HP at 40°F at this same flow is well within the allowable limits of the motor rating at this reduced flow and temperature. We would expect lower internal motor temperatures, which will actually increase your service factor in this operating temperature range (40°F). We have performed research at temperatures above and below 40°F with "No-Flow" and the motor has performed satisfactory. We anticipate no problem with your operating range.
Sincerely,
Kevin P. Price
Sales Manager
Sun-Star Electric, Inc.
RE: Well pump & pressure tank for fire hall
You are misinterpreting the data on the times for cooling. There are two factors that come into play for the cooling, ambient water and surface area. These motors heat up rapidly due to the amount of surface area available for cooling. Once they shut off, it takes time for the outer surface to transfer the built up heat out into the surround water. It is not because of the slow change inside the motor, but the limits of available cooling surface area. Flow at startup helps keep ahead of the heat, and actually does help slow the rise of the internal temperature to a degree (no pun intended).
When the ambient water is not flowing, the water in contact with the motor quickly rises toward the temperature of the motor. As the temperature of the water rises, the heat transfer from the motor to the surrounding water slows, thus slowing the motor cooling down.
The heat generated by a motor starting is always the same (assuming load, power, and other variables do not vary). Thus a motor at ambient will rise X degrees at start. If the internal temperature of the motor is higher than ambient, then it will be temperature over ambient plus X degrees at start.
Between those two items, you can not judge startup temperature rise and cooling needs based on the shutdown cooling rate. The heat transfer profiles are different between the two situations
The 6” motors from Hitachi have a different construction than rewindable larger sized motors available from Hitachi and other manufacturers that allows a greater internal heat rise, thus the letter that Sun Star sent you addressing a specific motor in specific circumstance.
RE: Well pump & pressure tank for fire hall
In the water well industry, these are standard motors in standard conditions and there is nothing specific about the circumstances.
RE: Well pump & pressure tank for fire hall
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Well pump & pressure tank for fire hall
It is the 6" that have the higher allowable internal heat rise, hence the higher ambient temperature rating for them.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall
If you overheat a motor with a canned stator, the stator will swell and grip the rotor, and the motor will never work again.
With a wet winding, when the motor cools back down, the stator will still be good and will work fine as long as the thrust bearing is not damaged.
RE: Well pump & pressure tank for fire hall
If you overheat a wet winding, there is a good chance you have done some damage, if not melted, the insulation of the winding wire. The temperature at which the standard wet winding wire starts to breakdown and melt is lower than the temperature at which the thrust bearing will usually lose its water layer due to the higher temps (depends on thrust loading). Heck, in a normal wet winding motor application, monitoring temperature is not really needed. Monitoring your voltage and current in all phases give you a quicker notification of when something changes. They can even be used over the life of the install to determine when the pump is wearing out.
RE: Well pump & pressure tank for fire hall
RE: Well pump & pressure tank for fire hall