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Old 05-22-2019, 10:03 PM   #21
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Join Date: Feb 2017
Location: Kennewick
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I deal with this on occassion with my greyhawk and was looking at the tank and lack of any space above it today. The post by Dancing Queen got me thinking.

If the tank is "siphoning", should it not stop when there is no ability to suck air into the tank? If all water intake valves are closed, then a siphon would create a vacuum (negative pressure) which should stop the siphon (finger over the end of a straw). This seems to be further supported by the post on turning on the pump breifly which would again...break a siphon as suction brings air into the hose.

I may be off base, but it would seem that the siphon then is created by one of the vent hoses, where the vacuum created would have to be offset with air from one of the other two vent hoses.

Perhaps blocking two of the vent hoses is the answer which would be a problem when filling (more volume/pressure in city fill hose than one vent could handle) but should not be a problem when using the pump.

2016 Jayco GreyHawk 31DS
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Old 06-15-2019, 04:23 PM   #22
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I just saw this, if this happens, switch to country fill for a 30 seconds or so. Fixed me right up. Or it was just a lucky coincidence.
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Old 06-15-2019, 05:47 PM   #23
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Originally Posted by matter View Post
I just saw this, if this happens, switch to country fill for a 30 seconds or so. Fixed me right up. Or it was just a lucky coincidence.
The problem is it can just start up again as you are driving down the road. Before I made the air gap mod, it would start every time I left the house or came back with a full water tank. The slope and corners I have in the driveway would slosh the water forward and to the corner where the vents are long enough to start the siphon.
Brian & Jeannie
2018.5 Seneca 37RB with to many mods to list
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Old 06-16-2019, 06:31 AM   #24
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Location: Southern Illinois
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As we are now in our 4th year of living in our Seneca, this has been a well documented and resolved problem through the help of many people here.
Within the first year, we realized what was going on with the syphoning impact and resolved by hooking all 3 vents together. I think I used a "Y" fitting and a "T" fitting to achieve this and then ran the single vent line to the driver's side into the "wet bay", where we terminated the vent with a valve. The drain then runs outside, right next to where I extended the fill hose.

Normal procedure is to fill until water runs out the overflow. Close the valve on the overflow and turn off the water filling the tank. There is enough expansion in the flexibility of the tank, that we can use the water in the system through the first day's use, including 2 showers. After using enough water to resolve the syphoning problem, I open the vent. Air rushes in and everything works normal, until the next fill.

We "boondock" quite often at rodeos and on the private grounds of clubs we belong to and want to carry the maximum water that we can. With the help of comments on this forum, we have achieved this and I thank everyone for their input.

Happy Father's Day, if it applies. I'm personally blessed with great kids and grand kids.
Smooth Sailing,
Ric and Jan Golding
Southern Illinois
2016 Jayco Seneca 37FS
2016 Chevrolet Traverse
2018 Cheverolet Silverado
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