Dual D5's - Series Question

[sn8kedr]

Hi lads. I'm planning on a serious upgrade soon and would like to build in dual d5 pumps in series to the loop. At the moment i have one variable speed d5 and one non variable speed d5 pumps.
My question is will the two pumps have any issues running in series due to the potential different speeds they will be running at?

[Dark NighT]

You should have the pumps on the same speed and everything will work out, i take it this is for your next project that is in your signature.

[alpenwasser]

In theory (yeah, I know ) the total head pressure (and hence total flow rate) should simply increase
and that's it.

However, what can happen if you hit the right frequency combination is that their combined sound
becomes rather unpleasant since you can get a beat (Wikipedia).

It shouldn't be a huge problem if you can adjust at least one of the pumps, you'd just need to change
the frequency of the variable pump very slightly since they really do need to be quite accurately
matched to each other for this phenomenon to be noticeable (especially if you've decoupled them
properly).

I'd say try it out, especially since you already have the pumps.

EDIT: Here's quite an extensive article on multiple pump setups, in which Martin mentions
this phenomenon as well IIRC (it's been a while since I've read it), although I don't think he calls it by
name.

[sn8kedr]

Originally Posted by Dark NighT

You should have the pumps on the same speed and everything will work out, i take it this is for your next project that is in your signature.

Yeah mate, this will be for the Danger Den build. I thought the same pump speeds would be ideal. Just unfortunate I have ended up with the two different ones.

Originally Posted by alpenwasser

In theory (yeah, I know ) the total head pressure (and hence total flow rate) should simply increase
and that's it.

However, what can happen if you hit the right frequency combination is that their combined sound
becomes rather unpleasant since you can get a beat (Wikipedia).

It shouldn't be a huge problem if you can adjust at least one of the pumps, you'd just need to change
the frequency of the variable pump very slightly since they really do need to be quite accurately
matched to each other for this phenomenon to be noticeable (especially if you've decoupled them
properly).

I'd say try it out, especially since you already have the pumps.

EDIT: Here's quite an extensive article on multiple pump setups, in which Martin mentions
this phenomenon as well IIRC (it's been a while since I've read it), although I don't think he calls it by
name.

Cheers for the info bud. I think I'll give these two pumps a shot as I should be able to adjust the variable speed pump to hopefully align with the non variable pumps rpm. Worst case scenario I end up replacing one of em to match

Has anyone actually tried a setup with two different speed pumps out of curiosity?

[alpenwasser]

Originally Posted by sn8kedr

Has anyone actually tried a setup with two different speed pumps out of curiosity?

Not yet, but when HELIOS is complete I will be able to adjust both pumps (D5) on a fan controller
independently, so I'll definitely play around with different rpm's and see what pops out.

[Bartacus]

Originally Posted by sn8kedr

Has anyone actually tried a setup with two different speed pumps out of curiosity?

I might be in this boat purely by accident. I broke the adjustment stick on one of my D5 varios, so it *might* not be running full steam like it's supposed to be. No issues yet, as far as I can tell, but I might only have one pump running at 4 - 4.5 instead of 5, so I wouldn't expect that to cause issues.

[B NEGATIVE]

Originally Posted by alpenwasser

In theory (yeah, I know ) the total head pressure (and hence total flow rate) should simply increase
and that's it.

However, what can happen if you hit the right frequency combination is that their combined sound
becomes rather unpleasant since you can get a beat (Wikipedia).

It shouldn't be a huge problem if you can adjust at least one of the pumps, you'd just need to change
the frequency of the variable pump very slightly since they really do need to be quite accurately
matched to each other for this phenomenon to be noticeable (especially if you've decoupled them
properly).

I'd say try it out, especially since you already have the pumps.

EDIT: Here's quite an extensive article on multiple pump setups, in which Martin mentions
this phenomenon as well IIRC (it's been a while since I've read it), although I don't think he calls it by
name.

The term is sympathetic resonance,my D5's get it in SR2 around setting 3.

You dont have to run the D5s at matching speeds either,D5s are a high bypass pumps,you are correct in saying that so fine tuning can eliminate the noise tho.

[sn8kedr]

Awesome, thanks for the advice guys. I'll give the different pumps a shot in the next few weeks and hopefully report back with no issues

Not that I think it'll make any difference but the plan is to run the variable first and then feed into the non variable.

[alpenwasser]

Originally Posted by B NEGATIVE

The term is sympathetic resonance,my D5's get it in SR2 around setting 3.

You dont have to run the D5s at matching speeds either,D5s are a high bypass pumps,you are correct in saying that so fine tuning can eliminate the noise tho.

Good to know, now I'm even more curious how my setup will behave. We actually had to do
quite a few problems in our physics course regarding this subject, those wave equations can
be quite a pain to solve.