The other weird thing is that when i test the griddle line when only my griddle in on, it is running at 9 on the WC. This is after the regulator to the main line and after the regulator for the appliance. Even when i turn on my steam table, the pressure for the griddle stays the same. But the second i turn on my deef fryer, the pressure drops to 1 on the WC. When all three appliances are on, the pressure in the regulator is at 12 on the WC, which makes no sense to me. Thats why i think something might be in the pipe. Our main line is a 3/4" black iron pipe i believe.
I assume this reading is at the griddle where the 9 WC was being read.
1st. What is the Brand name and model number of your Fryer? Then we might be able to located the installation manual.
Now you stated above the fryer was a 40 lb model, these are usually floor models with a BTU requirement of about 90,000. ... This gas demand by itself exceeds the rated capacity of a single 100lb tank in cool weather. ... Gas like water follows the path of lest resistance, the deep fryer is using all the available gas supply!
Since I don't know your specific fryer model, I will use the Entree model F-3
as an example. http://www.acitydiscount.com/Entree-40lb-LP-Gas-Restaurant-Deep-Fryer-w-Two-Fry-Baskets-F3-P.0.115504.1.1.htm
... installation manual, pdf http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&ved=0CFQQFjAE&url=http%3A%2F%2Fwww.avantcoequipment.com%2Fdocs%2FFF300-500.pdf&ei=1v9KUo-kGZa54AOikICoAQ&usg=AFQjCNHtmo_F506aW_vXID7eSPjxHdTyRA&sig2=2PcMoWRCxMwjwnwkXXuB2w&bvm=bv.53371865,d.dmg
Now this model & installation manual indicates the unit requires a min. of 10WC after its built-in regulator and the main supply line (3/4 inch) pressure needs to be 11 WC after an allowance of 25% pressure drop. Therefore, the min supply 'main' line pressure should be 15 to 16 WC (may be 18 WC) to insure the 11WC min at the fryer when it is on.
I would try setting the Fryer at about 7 or 8 WC (70% to 80%) to reduce the max BTU of the unit. This should help gas supply to other appliances, and reduce possible freezing at the tank. Once the oil is up to operating temp, I doubt you would notice little difference.
If your fryer doesn't have a regulator, it needs one (you haven't stated so above). Also, make sure an LP orifice is installed instead of the Nat Gas orifice. ... This example could be a lot different from your specific model, BUT I don't think so.