A Circulator Is Not A Pump

HeatingHelp

A bicycle pump is a pump. So is an oil pump on an oil burner. When those machines start, you expect to get a pressure on the outlet side of the pump that’s greater than the pressure on the inlet side of the pump.

A circulator is different because it’s working within a closed, pressurized hydronic system. It doesn’t have to lift the water to the top of the system because the water is already up there. The circulator doesn’t lift anything; it circulates. It’s very similar to the motor on a Ferris wheel.

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PETE_38

As I remember pumps produce flow not pressure, resistance to flow produces pressure.
I believe the circulator is a pump.

Jamie Hall

Nice. Black marks on the walls reminds you of hydronic heat? Um... well... OK! And for @PETE_38 , yes, technically a circulator is a pump, but they are built with distinctive characteristics and it would be quite wrong to substitute one for another. As to flow vs. pressure, pumps produce a pressure difference, which in turn produces flow. They will still produce a pressure difference, whether there is flow or not. It's a little easier to demonstrate this with a piston pump, as they can generate much higher pressures, but it's pressure first, driving flow. I can think of lots of examples of this.

unclejohn

Try lifting water up a pipe from a pond with a taco 007 and see what happens.

schreib

You make a good point about circulation, but if a rotating impeller creates a pressure differential . . . it IS a pump. Fluid will not move without a pressure differential or height differential. Pumps move fluids for BOTH reasons. There are many types of pumps: Positive displacement and centrifugal pumps cover 90% on the market. However, just because a CENTRIFIUGAL pump works to move water in a closed circuit does NOT make it a circulator. This type of pump is NAMED a circulator by marketing people responsible for selling low pressure head differential, centrifugal pumps to the HVAC industry. It is THAT simple.

Jamie Hall

To me -- being something of a pedant -- a centrifugal pump designed to be a circulator (it is not just marketing hype) is rather distinctive: it has, almost universally, a characteristically low, flat characteristic curve. Translation: the change in pressure differential with change in flow, which is inherent in all pumps which are not positive displacement, is relatively small (don't confuse this with constant flow or constant pressure, which is accomplished by varying the pump speed). This characteristic is achieved by the design of the impellor and diffuser of the pump.

Zman

This is a little like when people get all worked up over politically correct terms. As long as everyone understands the conversation and no one is intentionally insulting someone, I am good with it.

I have trouble not calling a big hole in the street with a steel cover a manhole. Probably because only a man would be stupid enough to go into one.

Circulatory and pumps are different to professionals, the terms can be used interchangeably when talking with a layman. Oh shoot, I did it again, I mean Lay"person"

Labenaqui

Not mentioned is the innate high bypass feature of a volute driven hydronic circulator at rest. We have demonstrated this attribute as a heating continuity feature upon circulator failure on our "Beta Sites".
Our recently patented "Neo-Gravity Hydronic (FHW) Heating Appliance(TM)" utilizes this attribute along with Delta-T Distribution Management to minimize energy consumption (8-13 Watts, typ.) in powered operation as well.
Natural (Gravity) Convection is always there, whether we opt to use it or not.

mike585

Pumps do work on a fluid. Pressure and flow depend on pump characteristics such as volute size and shape, speed, etc, and system characteristics. A circulator is a pump. When I worked in a nuke plant we had reactor coolant pumps in closed loops of pressurized water. They would be circulators given your definition. No difference.

EdTheHeaterMan

PETE_38 said:

As I remember pumps produce flow not pressure, resistance to flow produces pressure.
I believe the circulator is a pump.

I Believe that Pete missed the point.
a PUMP on a closed system is called a circulator because the "head pressure" does not need to account for "Static Pressure"

"Literary License" is used to make a point, however, the "Pumps" used to circulate water in a closed system can be far less powerful than one used to get that same water to fill up a swiming pool that is located on the roof of say... a hotel building.

I know for a fact that a circulator pump in a 5 story building has a head pressure of less than 8 feet even though the top radiator is over 45 feet above the circulator pump. In that same building, there is a Water Pump that produces over 65 ft of head pressure to get the water to the pool on the 5th floor.

Sometimes we can't see the forrest for the trees, me included. I just learned that many of the Wallies I thought were "Expert Posters" are not in the Trades, but are hobbiests with systems of their own that allow them to help others. Cudos to them!

Ed

PETE_38

It’s a pump, variable displacement type.

PerryHolzman

Its a pump. Just with low pressure head capabilities.

In the US Navy and in Power plants (not to mention Engineering School - I'm a mechanical engineer by training)... Circulating water pumps are common for cooling condensers, coolant system loops, Reactor Cooling in Pressurized Water Reactors (PWR), etc. They just have a low pressure head.

You cannot move water or any gas without 1st creating a pressure differential large enough to overcome the system resistance. It takes a pump to do that.

Have a great day,

Perry

unclejohn

It's a circulator. It is not interchangeable with a pump. You can not replace it with a pump that sits on the side of a cooling tower now can you. I mean you could but you would soon find out you have two very different things.

Jamie Hall

It's all semantics, folks. A pump -- a very general term, by the way -- is any device intended to create a pressure differential in a liquid (so as to distinguish it from a fan or blower). A circulator is a particular type of centrifugal pump. So is a ten stage deep well turbine. So is... It really does help to call a particular class of pumps circulators, as we all know what we mean (I hope). But for the fussy, it is also good to remember that a circulator is a member of the class centrifugal pump, which in turn is a member of a the general class hydrodynamic pump, which in turn is a member of the general class pump.

ratio

Y'all are missing the point. @DanHolohan can talk to engineers, who know that a circulator is a pump, and a homeowner who doesn't know the difference between a pump and a circulator. Not a lot of people live with a foot in both camps.

Dan (please forgive the familiarity), I enjoy your prose. Keep speaking to us!

DanHolohan

Thanks for getting it, @ratio

unclejohn

A jet engine and my lawn mower engine same thing right?

hot_rod

And to add more fuel to the fire 🔥 , there is really no such thing as head pressure.

 Got a pumper to put out the fire😉

What about a circulator pump? Covers both bases.

Jamie Hall

unclejohn said:

A jet engine and my lawn mower engine same thing right?

Insofar as they are both internal combustion engines, yes... otherwise, I sort of hope not!

Larry Weingarten

Hi, whether it's a jet engine or a lawn mower engine, the perspective from that blade of grass is probably a touch of apprehension. Not to try to put words in anybody's mouth, but I imagine Dan was sharing a different perspective also, in order to help people think and see the difference clearly. Good not to lose sight of that goal. I think perspective is a very powerful tool to carry around.

Yours, Larry

DanHolohan

Thanks, @Larry Weingarten. I spent my whole career listening to pros tell me that a pump will always raise the pressure at its discharge, no matter where you pipe it. 

Why?  

Well, because it’s a PUMP. That’s what pumps do. They PUMP. Pump means making PRESSURE. Always. And it comes out of the nozzle. It shoves the water into the compression tank. That’s why those old tanks waterlogged. 

Then their arms folded. Their heads snapped a nod. And they smirked. 

I watched that for 50 years. 

That’s why I wrote this story.
Thanks for getting it. 

PerryHolzman

Just put a differential pressure gauge across your "circulator" and you will see that it indeed increased pressure (even if that is measured in "Inches of Water" and fully meets the definition of a pump.

ChrisJ

This might be the most painful thread I've read on this forum............Dan deserves a hell of a lot more respect than this.

The entire point was the "pump" is moving a continuous loop, just like a belt or a bicycle chain. It's not lifting water. It's not behaving like a well pump. It's rotating a huge loop, what goes up goes back down etc. Of course the pressure on the outlet is higher than the inlet, otherwise nothing would move.

The point was to explain what it's doing to those who do not know or understand, not define a word.

Tinman

There’s head added and head loss. No head pressure. The circulator is the only thing that adds head. Everything else plays a part in head loss. Head loss and pressure drop are not the same thing. 

Tinman

Oh, and I interchange the terms all the time. 

EdTheHeaterMan

I this the same as the difference between Finnigan pins and Kronston valves? And which one are you supposed to use to check the blinker light fluid in your car?

https://www.youtube.com/watch?v=E6GsXhBb10k&vl=en

DanHolohan

I think you're supposed to use a pump to inject the blinker fluid.

I could be mistaken.

RobD739

The Taco 007-F5 circulator pump is one of the industry’s top-selling hydronic circulators, and for good reason.

RobD739

RobD739 said:

The Taco 007-F5 circulator pump is one of the industry’s top-selling hydronic circulators, and for good reason.

That's a Taco marketing statement. (Circulator Pump) 👍

EBEBRATT-Ed

It's the same pump/circulator. The difference is in it's application

Jersey2

They call the water circulator in a car a water pump.

EdTheHeaterMan

Jersey2 said:

They call the water circulator in a car a water pump.

But that is where the automotive industry is all wrong! See Dan's comment about the type of pump they use for blinker fluid.

HansonG

A pump becomes a circulator when it's in a closed system and it's discharge is routed (eventually) to its intake. Circulator, as in a CIRCLE. A pump is not a circulator when its intake isn't fed by its discharge. And I'm not an engineer or in the hydronics trade- just a guy who installed his own system which still works fine after 18 years.. I'm sure someone will want to chew on the details.. Have fun!

Lance

All pumps are pumps. How we use them is defined by their application or purpose. In our language we find shortcuts to speak, hence we skip the "pump" part and call it what it is for as all pumps are different according to their design. So do we say I want a pump and wait for someone to ask what kind, or do we just jump to what kind of pump we want? In teaching concepts though it is important to explain and think in the ways that make things different, how and why we use them. Dan always does a great job in his way of teaching. But I will ask this: When is a pump not a pump? When it won't work!

leonz

More fuel for the circulator/pump bonfire, don't yell too much.

www.sandpiperpump.com

www.youtube.com/watch?v=rICIBs34Uwo

Jamie Hall

I love all this. One miscellaneous thought -- one of the real advancements in the heating industry in recent years has been the introduction of ECM and other similar pumps, in which the speed of the prime mover -- the motor -- can be easily conrolled electronically over a wide range without major sacrifice in efficiency. Makes life much easier -- instead of selecting a pump best suited for a particular application, you select a generic pump and set the control electronics to fit its output to what is needed. There are still ways to mess up -- but it's a lot harder.

leonz

Well, then there is there are the Aermotor and Dempster "water pumping" windmills with its bronze pump cylinder that pulls water into the bronze cylinder through a foot valve connected to the sucker rod and on the down stroke the check ball closes and pushes this water up the drop pipe and on the down stroke it opens and lets more water into the cylinder and then it shuts the foot valve and pulls the water back up the drop pipe to the surface.

Jamie Hall

leonz said:

Well, then there is there are the Aermotor and Dempster "water pumping" windmills with its bronze pump cylinder that pulls water into the bronze cylinder through a foot valve connected to the sucker rod and on the down stroke the check ball closes and pushes this water up the drop pipe and on the down stroke it opens and lets more water into the cylinder and then it shuts the foot valve and pulls the water back up the drop pipe to the surface.

They're in the class of positive displacement piston pumps. Some of them -- if the rod is long enough -- can be used to quite astonishing depths -- a thousand feet and more in parts of west Texas and eastern New Mexico is not unusual.

leonz

Yup, they love the counterweight rocking horse/donkey/pump jacks in California near Santa Barbara and Texas oil fields like the black giant among other places worldwide.

jumper

Head/flow curves often differ. In a pinch a circ can do pump duty.

hot_rod

In a drainback type solar thermal system, the circ is actually lifting the water from the tank up to the collector. As such it could be called a sump pump, I suppose.

Once the siphon is established it becomes more of a circulator, just overcoming piping resistance. The system could be "open" or closed and pressurized and this works.

Lets call them circulator pumps.