On Monday, July 10, 2017 at 8:47:56 AM UTC-4, Ed Pawlowski wrote:
On 7/9/2017 10:53 PM, Stormin' Norman wrote:
On Sun, 09 Jul 2017 22:03:23 -0400, wrote:

On Sun, 9 Jul 2017 20:31:52 -0500, Dean Hoffman
wrote:

On 7/9/17 7:41 PM, Stormin' Norman wrote:
On Sun, 9 Jul 2017 20:32:51 -0400, Ed Pawlowski wrote:



I wouldn't, just a loop. Had dishwashers for 50 years and no problems
without it. Anyone know of a problem actually caused by a DW that back
siphoned into the water system? Yes, it can get into the DW, but the
purpose of the air gap is to protect the domestic water supply.

The air gap with a dishwasher prevents drain water from backing up
into the dishwasher and contaminating the dishes. Doesn't happen very
often, but if it does happen it can make people quite ill.

Not sure how a dishwasher air gap would protect the potable water
supply, but maybe.

I guess it's possible if the water supply pressure failed at the
same time.

Not likely with the design of those diaphragm valves, even if the
water supply was in the bottom of the dishwasher. The water pressure
is what opens the valve. No pressure and the valve slams shut. In real
life the sump of the dishwasher is air gapped from the supply line.

That was my understanding. Maybe Ed can explain the logic behind his
reasoning.


Not my reasoing. It is code in some places and their reasoning is if
the water system loses pressure the water in a running DW will not
siphon back into the water lines. Nor will it suck water from your drain
lines. It is the government saving us from ourselves.

I think it is way overkill and not needed.

I agree it's overkill, it's not required here in homes in NJ either.
If you look at the dishwasher install instructions, they say a high
loop is sufficient unless code requires an air gap. The high loop
works for me. It's almost as much protection as an air gap, without
extra, useless holes in the sink and more work installing.

However, I think Stormin is right, the purpose is to prevent waste
water from going into the dishwasher, where there may be dishes that
were already cleaned, not to keep waste water out of the fresh
water system. I can see how the former can happen, but not the
latter.