I think it would work if you put the check valves after the pump, but before the intersection of the two. Then a single pump failure would recycle back the failed pumps plumbing path. Good luck.
I believe that you could do that to prevent the backwash , but then again you’re also relying on a check valve to prevent a possible loss of both pumps. You would also need 2 check valves in that case. One just above each pump.
One thing I’ve learned is there is always more than one way to skin a cat .... or in this instance... plump dual pumps.
As 120 said, there are options here. I'm currently designing my plumbing, hence why I'm interested in the discussion. My tank has dual overflows, with two holes each. If I wanted to do a dual return, then I would sacrifice two of the holes and be limited to a Herbie overflow option. Then I could implement 120's design in my tank. However, I want a Bean Animal overflow, which means I only have one return pipe available. Therefore, if I want to run dual pumps, I can but should probably use DangerDave's suggestion of check valves after each pump and before the connection.
But there's also a question of why to do this in the first place.
I understand that having a backup to the "heart" of your tank is critical. You never want to be trying to get
Amazon to deliver another pump to you next day Saturday morning because the LFS is closed and your pump is out. But how critical is the return pump? If the pump only fails, you can stick your heater and an air pump in your DT and wait out the replacement. If you have a second one on hand, and you've plumbed in some nifty unions, you can easily replace the pump when it fails. This is useful for those of us who may not have room in the sump for a second pump and don't wish to run an external.
Really, the question is "will you know if/when your return pump fails." If your primary pump fails but you have a second one plumbed in as a backup, you may not know for awhile that one has failed but your tank is still running fine. If you don't have a second pump plumbed in, then failure to notice the failed primary pump could be critical to the DT.
I think this really gets at the heart of deciding whether to plumb in a second pump: what processes do you have in place to ensure that you know if equipment fails. Without good alarms in place to alert you if the primary pump fails, then having a second pump plumbed in is critical.
In my case, I'm using the new Neptune E832 bar, that monitors energy output. If I'm relying on Neptune to recognize the failure of the primary pump to draw power and trigger a process, does it matter if that process is a second pump coming on or an alarm to tell you to manually switch out pumps? The only reason I can think of is Murphy's law....that this will inevitably happen when you are not home and cannot go home anytime soon.
Please feel free to critique the thought process!
and I see what you mean, I should of wrote “pumps” ;Facepalm
