"Soft-Start" a pump with "pressure"?
Hello HeatingHelp.com community!
I am using four 7.5hp 3-phase 240vac self-primming pumps with foot valves to de-water our basement (commercial property built over an under ground spring)
I was pondering the use of electric power "soft-starters" ...... but the cost was an expensive option.
I never used such a large powered motor before ...... the sheer power is impressive indeed!
When these motors turn on, the initial machanical start up surge is quite evident.
For the pump to immediately force 27 feet of vertical standing water (15ft in suction and 12ft in vertical discharge) into a flow movement …. is very stressful on pump and motor.
In lieu of an electric "soft-starter" ...... I was pondering to simply inject street main water "pressure" (80psi) for 5 seconds on the suction side of the pump.
Adding this initial flow assist at start up …… the pump sees this standing mass of water …. already in full flow motion!
This should negate the mechanical start surge altogether ...... emulating an electronic soft starter.
........ thoughts on this?
Thanks!
Comments
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If your water flow from the domestic main were enough to spin the pump up to running speed — which it won't be; pumps make lousy turbines — there would be some benefit.
Much of the surge load come from simply getting the pump up to speed, not from starting the load.
You need motor starters made for those specific pumps. Don't cheap out.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
"If your water flow from the domestic main were enough to spin the pump up to running speed - which it won't be "
Agreed! …… but that's NOT what I'm doing! I'm accelerating the standing 27 feet of water to full flow for about 3 seconds. This represents the major portion of the "work load" surge to the pump and motor.
I don't even care if the impeller spins at all during this time! Motor is kicked in at the peak of my assist pressure flow.
Running the motor to spin the pump "un-loaded" the start up surge is hardly even noticeable!
Foot note:
My pump generates 50psi force against the water to obtain its maximum discharge flow ……. I would be applying 80psi lasting lets say 1 second to get this mass at rest to a more easily pumpable (less stress and force) moving mass.
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I didn't put much thought into it, but I think Jamie is thinking along the lines of how the pump works.
You're picturing getting the water in the outlet a head start and moving.
The problem is the pump doesn't care if the water is moving in the pipe. The pump's job is to get the water to spin in the housing, that's all. If you restrict the outlet of a centrifugal pump it actually puts less load on it. If you totally restrict the output it should put close to zero load on the pump. The reason is less flow through the pump means less water to get spinning.
I've personally watched the power consumption on my pool pump drop as I changed the return fittings to smaller ones. Centrifugal blowers work much the same.
More head pressure makes it easier on the motor, not harder. That's of course assuming you're using centrifugal pumps.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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A cheap chinesium 7½ HP 240V VFD is 2-300 bucks on teh internetz, well within the range for experimenting. You can, of course, pay more for one. I personally like the ones with built-in bypass contactors for critical duty. You also gain the ability to turn down the pumps to meet demand, as well as the ability to lead-lag or round-robin the pumps for wear leveling and other clevernesses.
I really think that a bailing wire and duct tape approach to your problem isn't going to serve you very well over the long run, unless failure isn't a big deal.
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If your pumps are self-priming why don't you try removing the foot valve from one pump and let the pump and line drain when the pump shuts off. You will get rid of the standing head
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Soft start each motor one at a time.
It is correct that »More head pressure makes it easier on the motor, not harder. That's of course assuming you're using centrifugal pumps.« If you can devise a way to do this you reduce starting current surge somewhat.
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You still have and will continue to have the 150% of actual amperage at start up for each electric motor so keep that in mind as that never changes.
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"A cheap chinesium 7½ HP 240V VFD is 2-300 bucks"
….. you have a link to that pump??
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The foot valve affords for immediate pump flow ….. self priming can take up to 1.5 mins before it pumps water (20 ft suction pipe).
They pump has an internal flow check to keep the discharge head.
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"If you totally restrict the output it should put close to zero load on the pump. The reason is less flow through the pump means less water to get spinning".
…… first, you do understand my set-up here has both a totally flooded suction and discharge piping 24/7 ? ……. right? (foot check and a closed discharge valve)
so, if I understand what your saying, I can run this 7.5hp pump with the discharge valve closed? ….. and the pump sees "no load" to expel its energy into?
….. you really don't think that the spinning impeller vanes will now act to hydraulically compress the entrapped water its encased in? Very little work but extreme energy being converted to heat and bait conditions for cavitation? (dead heading the pump)
A dead-head is when a centrifugal pump operates with no flow through the pump due to a closed or blocked discharge valve. The pump will recirculate the same water, causing the water temperature to rise. The excessive heat produced can damage expensive seals and significantly reduce the life of your pump.
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No,
There's no extreme energy being converted into heat and you cannot compress a liquid.If you leave the pump running for a long time the water will get hot from friction. You're not going to get cavitation from restricting the outlet.
What I said previously is accurate.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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For a few examples. These are most assuredly not ABB or Mitsubishi drives, so I wouldn't stand right in front of it when I first apply power, but they're so much fun.
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Look up "The spruce goose" airplane (Howard Hughes), he used water for the hydraulic controls system …. he found out the hard way that water is in fact compressible!! It shuttered so bad from the compressibility of the water …. he never flew it again.
"You're not going to get cavitation from restricting the outlet".
well, you agree that its going to heat up the water …. right?
Let it reach 213 degrees or higher and you now have super heated water! Hello cavitation !!
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Good grief.
I think I'm done with these discussions at this point.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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That is not why the Spruce Goose only flew once.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
…… and you do realize that the motor windings have to be VFD rated for the heat? ……. that's a more expensive motor just for starters!
I'm not connecting that cheap $169 VFD to my $1,500 motor thank-you! ….. especially with your warning "stand back when ya plug it in" : )
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…….. your on! : )
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The Spruce Goose (Hughes H-4 Hercules) flew once, and only once. Although she never left ground effect, the pilots were, by most reports, quite happy with the way she handled.
She did not, however, have an airworthiness certificate — and although Howard Hughes was never too concerned about such technicalities — and was a fine pilot, by the way — but he was trying to get some money out of the Feds to pay for the thing, which he never did, and so was not inclined to bust too many rules.
Oh and aside — all liquids are, in fact, compressible — just not very much. Hydraulic fluid is no exception. Once a hydraulic system is fully pressurized — whether it is hydraulic fluid, water, good single malt Scotch, whatever — no further compression will occur.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
https://www.precision-elec.com/shop/acs580-0p-024a-2-f255-g310/
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A VFD is what you need. Any three phase motor will work with a VFD they may not last as long. Check the motors you have they may already be VFD rated.
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"Although she never left ground effect, the pilots were, by most reports, quite happy with the way she handled."
mmmmmmm …….. I wouldn't trust any pilot that acclaims, was "very happy with the way she handled" ……. for a plane that never left the ground! (sounds more like PR for Howard than a flight performance report)
……. would you??
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….. how did we go from just $200 to $300 ….. to $4,000 ?? : (
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It's an ABB drive with bypass contactors in a NEMA 1 enclosure, not a bare chinesium drive. Don't forget to check rotation on both the drive and the bypass!
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Ground effect is very different from ground, @RickDelta — if you don't know the difference, please don't try to fly an airplane. And Howard Hughes, at that time in his life, was a very fine pilot, and the rest of the crew on that flight were equally well qualified.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Upstream from you. Even has a forecast.
https://water.weather.gov/ahps2/hydrograph.php?wfo=phi&gage=tren4
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Ok! ….. I think I got the perfect solution for this "Pressure Assisted" soft start for large water pumps.
Its the "I-Flush" version (solenoid operated) to the "Flush-a-Matic" power flush!! : )
It uses the street pressure to compress an air storage tank and is released on demand by a solenoid operated large port poppet valve.
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Variable speed belt drives, anyone?
Cheaper to maintain than starters.
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…… like a Continuously Variable Transmission (CVT)?
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Pondering ….
There are documented accounts of large ocean tankers that suddenly lose all their buoyancy at sea and drop to the bottom of the ocean like a rock!
They attribute this to a large release of gas bubbles from the ocean floor. The bubbles reduce the density of the water in that area and the ship sinks.
At run time for my large water pumps, the 12 feet of "standing" water in the vertical discharge pipe offers great resistance to the pump from its parked location, to being immediately forced up and out the pipe (Newton's first law of motion).
My thoughts are if I were to inject an air stream (bubbler) into the pipe on the suction inlet port, greatly decreasing the density of the surrounding water flooding the pump impeller …….. this would have the effect of releasing the pump impellers from the immediate load demand (surge reduction) and time to come up to speed un-loaded …… a soft start!
….. thoughts on this?
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Please buy the book on pumps that I mentioned. You still have the 50 percent greater amperage draw at start up no matter what resistance there is from the standing water column in the chamber and if you introduce air in the chamber the tips of the volute will heat up and the pump will cavitate.
As I explained in great in great detail to you a double diaphragm pump pushes water mass against water mass for thousands of feet with little energy used by using a very low amount compressed air to push the diaphragms back and forth at low and higher pressure.
The 4 inch diameter load of water being pushed pushes against the water or mud ahead of it to move it at a desired volume with very little energy expended per minute equal to a centrifugal pump of the same volume.
If in the case of a gas bubble "coming under the hull of a ship" the bouyancy of the ship is compromised as the ship "may" drop into a bubble only if it is massive and charged in enough pressure; but you are forgetting compressed gasses reaching near sea level pressure of one atmosphere PSIG have less pressure per cubic inch. Low pressure gasses like water and electricity both are lazy and will go everywhere and anywhere if not contained and the closer to the surface a gas reaches the bubble disperses. The same thing occurs with dive bubbles.
I do not believe that anyone that could have survived a massive failure like this has been rescued and lived to tell the tale due to blunt force trauma and drowning in the ship cabins one would assume when the glass windows break as the ship sinks so it is a case of speculation and hypothesis without a conclusion because a great deal of the reason for a ships loss is never determined.
The other thing is the ocean water will immediately occupy the space the gas exits at the surface from due to its mass and volume.
Bringing up another case of a giant gas bubble is Lake NYOS in Cameroon. This fateful gas bubble erupted from the crater lake bottom on 21, August 1986 which is covering a dormant volcano rolled down the mountain due to its density and killed farm animals and 1,700 people in the village that were outside, the villagers that were inside their homes survived because of the oxygen atmospere in their homes.
Another instance is Lake Monoun another crater lake in West Cameroon that killed 37 people on 15, August 1984.
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You really need to research how centrifugal pumps work. That's where to start.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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.... thanks to HotRod!
Your recommendation for the auto-fill have worked perfect!
This non- self priming centrifugal pump now emulates a self-primming pump with 100gpm more flow than the self-primers of the same hp!
..... this pump is suctioning water 15 feet below it and discharging it verticaly 12feet up and out @ 350 gpm!
..... not bad for a new $1,500 pump we got at auction for $25 (damaged) ..... I repaired it with only 4 fender washers!
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@leonz
"You still have the 50 percent greater amperage draw at start up .… "
Agreed! ...... I remember "Eli's Ice Cream" very well from electronics class! (by 90 degrees) : )
....... the "bubbles" won't cavitate at all!
Ever see a "bubbler" in a fish tank? It simply airates the water and floats up and out to the top!
If it were cavitation...... all the fish would be dead!! : (
It's just a simple solution to relieve the working load on the pump until it gets up to its optimal pump curve position.
...... you could do the same with a magnetic clutch drive ..... but that is a costly option.
Foot note:
In repairing this pump I had the remove the pump from the motor. After repairs, I powered up just the motor without the pump attached.
It's 3- phase 240 vac @18 surge and run @16 amps.
Running the pump only like this, unbolted to anything! ...... it doesn't even show any motor torque in its body.
When the motor is attached to the pump ..… a slight rotational torque is evident in the motor body.
With 15 feet of water at rest in the suction (foot valve check) and 12 feet in the discharge pipe ..… at start up, there is a dramatic torque evident in the motor (start-up stress under load).
I eliminated this rotational motor case torque with 3/4" all thread connecting all these very heavy motors together as one mass.
This is why I seek to relieve the motor and pump from this stressful and damaging start up condition.
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"I've never seen a centrifugal pump that could create enough of a vacuum to do that. Especially single stage." - Chrisj
...... LOL!!! : )
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"I've never seen a centrifugal pump that could create enough of a vacuum to do that. Especially single stage." - Chrisj
...... LOL!!! : )
"No,
There's no extreme energy being converted into heat and you cannot compress a liquid." - ChrisJ"Oh and aside — all liquids are, in fact, compressible …… " - JamieHall
"If you leave the pump running for a long time the water will get hot from friction" - ChrisJ
ROTF LOL !!!!
Foot note:
To better understand this issue of a fluids compressibility, both oil and water have almost equal compressibility properties (very low compressibility).
The problem with water in its compressibility is that water easily mixes with gases (like air!) ….. dramatically increasing its compressibility as an effective hydraulic fluid.
If you ever changed the hydraulic (oil) brake calipers on your car and didn't "bleed" the air out of the brake lines, the brakes control response to your pressing on the break pedal is poor and spongy. This is because air is very compressible!
This was what Howard Hughes experienced in his "Spruce Goose" airplane, the hydraulic (water) system used had gas (air) dissolved in it!
This caused the flight controls to shutter making the airplane unworthy of safe flight.
I'll bet this is why he never again attempted flight in this airplane.
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My dear man. I have several thousand hours of flight time in my logs, on everything from J3s to F4s, and I have never yet heard the term "shutter" applied to an airplane's behaviour. Would you kindly enlighten me from your store of knowledge?
And I explained to you why the H-4 only flew once.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Cavitation and Aeration are 2 completely different mechanical occurrances.
Cavitation in pumps is "the rapid creation of and subsequent collapse of air bubbles in a fluid".
Aeration also called aerification is "the process by which air is circulated through, mixed or dissolved in a liquid or substance". Two examples of this are air entrained readymix concrete and aerobic digestion in sewage treatment.
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this conversation brings back this memory:
Retired and loving it.
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@JamieHall
"I have never yet heard the term "shutter" applied to an airplane's behaviour"
"shutter" is a shaking or vibrating condition (think: a stick shaker in an airplane …. you do know what that is …. right??)
…. or think of the effects of aerodynamic buffeting …… it can violently shake the airframe into failure.
…. so, lets say your on break up in the crew's rest area of a 747 and your co-pilot pages you "Captain , the control stick is shuttering violently" you would have no clue of what he's talking about?? ….. you would just go back to sleep??
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omg
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
2
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