A question in Industrial Pump Piping

[ewokxz]

Here's a question I would like to ask regarding industrial piping connections. There's this design I found stupid... or its me that's stupid, so kindly enlighten me. The pump is supposed to be installed with a BALANCING VALVE in its discharge end (huh?).... i mean... what function does this do to the system.... engineering wise..... help this stupid guy please...

In an installation when you already have several AHU and FCU connected with line Balancing valves, i dont see the point in having a balancing valve exactly as it is in the pump... I mean for what?

thanks

Vertical Pump Piping copy.jpgEnd Suction pump piping copy.jpg

[MikeHolm]

Does the system employ primary/secondary piping? In other words does this pump just circulate within a space and the other smaller pumped loops take the heat to the AHUs?
My first thought is that the designers didn't want to pay for a VSD on the pump so they put a balancing valve on it.

Second, if you are concerned about the placement of the valve, this pump needs to maintain a "net positive suction head" or it will start cavitate and destroy the impeller as well as cause other pressure problems upstream. We do not put balancing valves on the suction side of the pump as we try to allow for as much free flow into the pump as it needs to not cavitate.

To say more, we would need the pressures on both sides of the pump and the placement of the tee for the expansion tank.

Cheers.

[Magoo]

Balancing valve is to control the flow to the system, setup at commissioning and usually locked in fixed position. Sometimes just a butterfly valve, other times a stat regulating valve, can also be a motorized valve with min and max settings controlled by a down stream pressure transducer for vaiable flow systems.

[Brian_UK]

The balancing valves around the systems, AHUs and FCUs, are just that, for balancing the flow rates in the correct proportion with relation to the design flows.

The flow regulator on the pump outlet to to regulate the total flow to the system.

As mentioned above, the ideal would to a variable speed drive or even a belt drive where you could alter the speed with pulley changes.

[Segei]

Usually, these valves control maximum flow to prevent motor overload or lost prime.

[ewokxz]

Does the system employ primary/secondary piping? In other words does this pump just circulate within a space and the other smaller pumped loops take the heat to the AHUs?
My first thought is that the designers didn't want to pay for a VSD on the pump so they put a balancing valve on it.

Second, if you are concerned about the placement of the valve, this pump needs to maintain a "net positive suction head" or it will start cavitate and destroy the impeller as well as cause other pressure problems upstream. We do not put balancing valves on the suction side of the pump as we try to allow for as much free flow into the pump as it needs to not cavitate.

To say more, we would need the pressures on both sides of the pump and the placement of the tee for the expansion tank.

Cheers.

This CHW pipeline route goes from/to the chiller then there is a secondary "booster pump unit to increase the head, but basically this is a single line loop with the return line passing to a Hex upon return to the machine room to reclaim some heat.

What I am after is whether in basic single line flow of the CHW piping system, what pros and cons does putting a balancing valve entails to the system? Basic installation would be RETURN PIPE-STRAINER-PUMP-CHECK-CHILLER-SUPPLY PIPE-[]-STRAINER-MOTORIZED VALVE/BALANCING-RETURN PIPE (LOOP)

[MikeHolm]

Strainers are often on the suction as are check valves (which could go anywhere, almost) as their pressure drop is well defined and accounted for.

balancing valves especially motorized ones can reduce the pump head so that the booster is needed at different times (don't know the vertical distance or operating pressures of the system). Most pumps are not built to operate well with the suction at near atmospheric so i don't advise it. The pump can only put out so much head pressure and you can either "take it away" from the system, by increasing suction pressure drop or "add it" to the system by decreasing suction side drop.

If, for example, the system was a single loop at one level operating at 2bar static and the pipes were 200mm AND the flow rate was within the middle of the pumps curve, you would have no problem with the valve on the suction. If your piping was going up 5 floors and your pump was operating at a point closer to the limits of the curve, reducing the flow with a suction side valve may drop the output pressure enough that the booster pump up higher would be needed.

The other factor is the exp tank and its placement, which I hope is teed in on the suction side of the pump as well. That's my opinion. Basic rule.....pump into the pressure drop, don't pump from it. Works every time.

[ewokxz]

Strainers are often on the suction as are check valves (which could go anywhere, almost) as their pressure drop is well defined and accounted for.

balancing valves especially motorized ones can reduce the pump head so that the booster is needed at different times (don't know the vertical distance or operating pressures of the system). Most pumps are not built to operate well with the suction at near atmospheric so i don't advise it. The pump can only put out so much head pressure and you can either "take it away" from the system, by increasing suction pressure drop or "add it" to the system by decreasing suction side drop.

If, for example, the system was a single loop at one level operating at 2bar static and the pipes were 200mm AND the flow rate was within the middle of the pumps curve, you would have no problem with the valve on the suction. If your piping was going up 5 floors and your pump was operating at a point closer to the limits of the curve, reducing the flow with a suction side valve may drop the output pressure enough that the booster pump up higher would be needed.

The other factor is the exp tank and its placement, which I hope is teed in on the suction side of the pump as well. That's my opinion. Basic rule.....pump into the pressure drop, don't pump from it. Works every time.

I am a bit lost with this one sir, kindly clarify, the balancing valve is located at the discharge side of the pump. In no way that I will be putting it on the suction.
Based on the curve with the current selection - the head vs flow is converging directly near the apex of its curve at 67 eff rating. Basically put, its the maximum effective supply of the pump. That is why I worry. Based on the explanation I have (some basically got lost in translation ) the pump do not have VFD and will run at its full frequency (50Hz) so - quoting from your previous reply

My first thought is that the designers didn't want to pay for a VSD on the pump so they put a balancing valve on it.

... I may say this is the reason why.

But then again, I have this issue about the head of the pump. If the head is enough to push the water up to the last unit - hitting the curve end thus the return pressure will be so low that - yes, the pump could have a suction pressure almost at the atmospheric level. I have to make a viable calculation with this one myself. The designer is only content with what he has already given (like most designers do)

...and oh btw, the installation will serve a hotel 7 and a half floors with the pump room at the GF, each floor having half a sq.hectare effective area.

[McFranklin]

It is a well accepted design, the balancing valve is to regulate the pump output. Then at each individual branch or load you place another balancing valve to control that zone. I try to use triple duty valves, a combination stop-check-balancing valve. They can take up less space, but mostly there are fewer connections. Whether they are flanged, threaded or welded. I work the construction side, so fewer connections mean a faster install.

[slalomguy]

Waste of money and energy to have a reg valve on the pump discharge if you have reg valves on the AHUs.
Not a substitute for VSD either.

[McFranklin]

Yes, by their very nature discharge throttling devices will move the pump to a less efficient point on their curve.
However, it is the most common and cheapest method of regulation. The regulator at the pump regulates the entire system flow to prevent the pump from running out the end of the curve. The regulators at the AHUs regulated the flow to that unit, which may or may not be operating.

The original poster was from the Phillipines, when I was there in the 1980's the electrical power system was not the most reliable, if that is still the case and the installation is located there, it may be a factor.
The last time I did a comparision a VFD drive added 750-1000 USD per motor horsepower.

In an ideal world the system would have VFDs on everything with an building wide control system, but the owners may not want to make that kind of investment.
And balancing valves are a well established technology, set it and forget it. Without an economic study it is impossible to say that the VFD is the way to go, based on a benefit versus cost.