Where is your low flow shut off tube installed?

[danno]

The tube that goes to my low flow shut off switch comes off right at the output side of my low flow pump. The problem I'm having is that my sap filter is mounted after the low flow tube.

So ... when my sap filter plugs, I still have pressure at the low flow pump, and thus pumps don't shut down and high pressure pump continues to run even though no sap is moving through it. I can't imagine that's very good for it.

Any reason why I should not move tube for low flow switch to between the filter and the HP pump?

[Bucket Head]

That does not make sense. Did someone alter the plumbing before you got the machine? It almost sounds like it. Mine has that tube on the "out" side of the pre-filter housing. There is a "T" fitting on the high pressure pump feed line for this tube. That would be the only way it could sense a low flow because of a clogged filter. Hopefully some experienced RO guys will chime in here, but it seems like it is plumbed wrong.

Steve

[802maple]

It should be after the filter.

[danno]

Thanks guys - that's what makes sense to me. I just took a look at the manual. This is a 20 year old machine and the low flow switch was not part of the original design. It must have been added later at the wrong spot. Neither pump is original.

HP pump seems to be working OK, hope it's not dmaged from running it dry.

[802maple]

You should be fine as the pumps on your machine can run dry for a period of time. On the new machines if the high pressure runs it will take out the mechanical seal on the high pressure and recirc pumps in a heart beat.

[TunbridgeDave]

Been trying to read some of your older threads Danno and my low pressure tube comes out of the low pressure pump also. Everything is original on this machine. Did you relocate the tube after the filter?

[danno]

Sure did, Dave - and it works much better. Now when filter clogs, there is no more pressure on the switch and both pumps kick off.

This was also one of the reasons I suggested the longer filters they sell - my short filters used to clog pretty quickly, especially late season.

I also have really lousy pressure coming off my low pressure pump to begin with, and I'm sure that did not help those filters from cloging. Turns out the guy who had the machine before me got a very expensive medical pump at a great price to replace the original low pressure pump. It's a sweet stainless pump, but with the current impeller, it's only designed to reach a max of about 20 PSI with the low flow into the membranes.

[TunbridgeDave]

Thanks Dan, with your help I'm hopeful this machine will work out well for us this next season.

[TunbridgeDave]

Hey I thought of something else. What about putting a pressure gauge on either side of the pre-filter? Then you would know what kind of pressure drop you're getting through it and thus, when it's time to change the filter.

[danno]

Hey I thought of something else. What about putting a pressure gauge on either side of the pre-filter? Then you would know what kind of pressure drop you're getting through it and thus, when it's time to change the filter.


That's what I wound up doing and like that system with multiple guages. In terms of when to change the filter - if you're not watching the machine, pumps will simply shut off as long as your low pressure cut off is after the filter. If you are watching the machine, when the filter begins to plug, it's not too gradual, pressure drops in a hurry.