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.

Steve Minnich

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. 

Steve Minnich

Oh, and I interchange the terms all the time.