6800RPM gear pump too noisy for residential market. Box?

[stabmaster]

I have this solar thermal recirculating pump that meets all necessary spec's (1 GPM, 20ft head, and 35W solar panel). All of this but it is too noisy for residential use at 6800RPM. A high pitch whine is unacceptable on a quiet day.

I've tried different boxes. The more deadening, tigher seals, and more rubber mounts the better; however, it is beginning to look a bit too complicated.

I haven't found much by way of pump mounts so I'm using a pipe hanger and EPDM rubber to mount the pump. This is robust but simply doesn't look production worthy.

Here is the pump:

http://www.fluid-o-tech.com/files/MGBR1.PDF

Any ideas for cancelling the noise?

 

[ClicketyClack]

Find a pump that you can turn slower.

 

[BigInch]

I would not think that a 6800 rpm pump would be very reliable, if it was produced cheaply enough for the home market. Sounds like a good way to develop lots of angry customers.

http://virtualpipeline.spaces.msn.com

 

[ClicketyClack]

I second that. I don't understand how at this speed the cavity between the gear teeth could even fill with fluid.

Maybe it's a torque issue? Why not then use a centrifugal?

 

[HEC]

Good point ClicketyClack, the excessive noise may even be due to the lack of fluid filling between the teeth!

Mark Hutton

 

[stabmaster]

unfortunately, it requires a 1/3HP centrifugal pump to overcome a 20ft head. Also, the pump can't be mounted above the fluid level without a snorkel or trombone or something of that sort. Extra traps and valves cost money and lead to more failure and uncertainty. If we manufactur these than we are trusting plumbers to install them correctly.

Believe me, we've been using centrifugal pumps for 20 years.

Since the control is via photovoltaic, at $5 per watt energy comes at a high premium. I realize we're engineers but product differentiation is important as well as curb appeal (solar driven pump, no wasted watts).

the only solution for a drainback system is positive displacement. I had considered rotary vane or sliding vane pumps; however, i can't seem to find magnetically driven vane pumps that meet the specifications. the high RPM IS what makes the product work. The noise is an externality and should be a solvable problem. It's not incredibly loud.

since this bldc driven pump is a retail $450 unit, it is not exactly a piece of garbage. The custom built controller is designed to operate this pump at less than full rpm. Much of the time this pump will operate at under 3000 rpm. The estimated life is over 30,000 hours (or according to the manufacturers, "forever") and the estimated daily operation is 10 hours.

So on the noise issue.. anyone tried to tackle this?

 

[dickon17]

Did you ever consider an Oberdorfer gear pump?

 

[hydtools]

How is the pump connected to the system? Reinforced hose or hose without reinforcement?

You are not dealing with very high pressure. Use soft hose or tubing of a larger diameter than you have now. This would attempt to reduce the plumbing response to the pump frequency.

Ted

 

[stabmaster]

hydtools

you're absolutely correct. I've been using automotive rubber hosing for the input. Initially we went with this. Then, we decided that plumbers would have a fit if they noticed something that wasn't a standard plumbing connection. Finally, we decided that they will have to deal with it. However, on the exit side we're using braided rubber "under sink" type compression hose.

dickon17: never heard of an oberdorfer gear pump...

 

[stabmaster]

edit: looked at oberdorfer. looks similar although the pumps available appear to reach 1gpm only with 120 watts or so, unlike the fluidotech pump that i found which requires a mere 35W.

 

[ClicketyClack]

Where are you now with the noise and where do you need to be?

 

[dickon17]

According to the performance curve, an Oberdorfer N1000 at 800 rpm will give 1.0 gpm at 20 ft for less than 25 watts.

 

[EdStainless]

For high freq noise this is an isolation issue. It sounds like your mounting is still too stiff. If you were having lower feq noise issues I would suggest active noise cancellation.

Keep looking for lower speed pumps though, they will be more reliable.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[ccfowler]

You may want to take a close look at mounting diaphram type pulsation dampers immediately adjacent to the suction and discharge ports of the pump (the closer, the better). Gear pumps usually have significant flow fluctuations at a substantial multiple of shaft speed (a function of the number of teeth on the drive shaft gear) that do a nice job of making noise. The pulsation damper at the suction port can be particularly helpful if there is an NSPHa vs. NPSHr problem (fairly likely due to the high shaft speed).

The type of gear pump matters very much, but it was not clear to me which type of pump is involved here. It looks as though it may be a crescent type (which usually produce milder flow fluctuations compared to most other gear pumps). Being a crescent type pump may account for the high shaft speed being tolerable at all.

 

[stabmaster]

dickon-

thanks! i talked to oberdorfer and got ahold of a lip-seal type which i was told has very low drag. the packing they normally use to "seal" the pump is designed to drip. intersting.

anyways for $168 it seems pretty tasty. brings production costs down 20% on the motor/pump assembly. if it will do the job at 25W it brings the PV requirements down about $40. definitely worth checking out!!!!!!

thanks again.

 

[ClicketyClack]

Packing is almost always "designed" to drip.

 

[stabmaster]

It is apparently impossible to find a BLDC 1/16hp (circa 35-60W) motor that runs in the correct rpm range (800-1750rpm or so?)....

and if i do (bodine-electric) its commutated at 60 degrees instead of 120, and its $232!!!!!! yikes!

i think that Papst may have one but they're impossible to deal with! lol.

 

[dickon17]

Did you consider Anaheim Automation for one of their BLDC motors with integral reduction gearbox?

 

[chief]

Consider a Switched Reluctance Motor. You will get a high speed without the need of a gearbox. They have now solved the noise problem on these motors. Costs are something I am not aware of at present.

 

[Tmoose]

Does the whine only becom objectionable at 6800 rpm?