This information is a combination of Web Site research, Testing different POL (Prest-O-Lite) fittings with flow measuring equipment, and interviews with various people in the propane service and sales in my area.
I am not an engineer, and anything I state in this report should be verified by other sources. I have been wrong before, and it could happen again.

If this is not the Information you are looking for check out these  sites, They are Commercial sites that also offer very good explanations of Propane , and Propane Products. i highly recommend these two sites.

WWW.Propane101.com

WWW.Propaneproducts.com

The OPD valve has been blamed for many problems relating to propane appliance malfunctions. I have mistakenly done this on numerous occasions.

I would like to start with one of the reasons for this.  It is the direct result of "resistance to change". I do not think I am alone in this "Attitude" of, "Why do I have to change my tanks to the new OPD valves when I have had no problems and know what I am doing!  Well the truth be known, I really did not know all that much in the 1st place. This past week I have modified that knowledge base.
The test were done on a cool windy day away from homes, The test cylinder was just over ½ full, and after testing,  the cylinder was filled and most tests were redone. There were no noticeable changes.

OPD Valve See Exibit

The Float Assembly, is the part of this valve required to meet the NFPA 58 requirement dealing with an automatic overfill protection. When the liquid level reaches the float the scale setting should already be reached, or the manual overfill(80%) valve would be spitting liquid indicating the cylinder is at maximum fill. This floats function is to stop the fill process only when the scale method is wrong, and or the manual (80%) valve is not used.
There has been some information as to this assembly would shut the cylinder outflow if the cylinder was tipped. From the experiments I have preformed with 2 different 20# cylinders, this does not appear to be factual. I initiated vapor flow with an open POL fitting and while vapor was being release into the air, I tipped the cylinder 90 deg. two different ways (right and left), and totally upside down resulting in liquid being discharged from cylinder each time, and with both test cylinders. This is not to establish that there are no OPD valves in use that will not close when tipped as this function is discussed in several information sites. http://www.propane101.com/opdcylindervalves.htm

The Excess Flow , This next test was to investigate the excess flow shut off that is discussed in several web site information pages. This feature is believed to stop vapor discharge in the event of a leak, (hose, fitting) etc.
When testing this feature a through flow(unrestricted) POL fitting was used and a flow meter was installed in line and a 3/8" ball valve was incorporated to simulate a broken fitting or hose.(see exhibit A). With the hand wheel valve fully open, and 30Lpm(liters per min)(this was the only flow meter I have and know that propane flow values are described indifferent ways) again flowing 30Lpm through the discharge the ball valve was then opened fully. When this was done I anticipated the valve would shut off, But the flow was initially increased, then reduced some, and in no way did it stop. The discharge was still in excess of 30Lpm on the flow meter while vapor was discharging through the ball valve also.
The next test was done with the cylinder outlet discharge check held in the open position with 3ea 5/16" flat washers stacked and held with the swivel nut only from a POL fitting. The cylinder was opened slowly, and vapor discharged into the air. When cylinder valve was opened just beyond the 1 full turn and vapor being rapidly dispensed, there was a sudden decrease in flow and further opening of the discharge valve made no difference in flow rate. So there is a excess flow reducing function of these valves, But they will still dispense a large amount of vapor, or liquid if tipped. This is something that would happen if the cylinder was attached to a hose and the hose then attached to a pressure regulator, and the hose was cut or burned open or off. But in many applications the POL fitting is attached directly to the regulator, and then the regulator becomes the overflow device.
However the regulator could fail and excess flow could be delivered to the appliance resulting in serious problems. We will discuss Excess flow POL fittings in another chapter.

The Discharge Check Valve, prevents any discharge from the cylinder unless there is a POL or Acme fitting connected to the valve. This feature has been discussed as being a suspect problem on web site information pages dealing with poor flow/discharge from cylinder. www.bluerino.com/
My test of this feature was to run a turkey cooker burner at full regulated flow and loosen the POL fitting until there was a decrease in flow. I was able to back the POL swivel nut away from the valve 2 full turns before the flow began to diminish. This was done with a POL fitting that has an O-ring seal, and there was no noticeable(bubble test) vapor leak while loosening the swivel nut.
I then reversed this test by opening the cylinder hand wheel and then tightening the POL fitting. The vapor flow started and was flowing sufficiently with more than 1-1/2 turns away from full engagement.
With this finding I find no merit in the information on BlueRino web site.
ADDED Aug 2018;
a reduced flow could be the result of a tripped excess floe valve or a tank adapter with an excess flow valve that delivers a lower BTU flow than the appliance requires.
Acme fittings will have excess flow where PLO fittings come with full flow or excess flow valves!
 

The manual overfill valve, also known as the 80% valve is basically unchanged from the old style cylinder valve,
The Drop tube, associated with this valve will discharge vapor until the liquid level reaches the tube (indicating the cylinder is 80% full(the maximum safe fill for all cylinders)), and at that point liquid would be seen spitting from this small vent. This valve can also be used to vent cylinder to atmosphere, in the event of main valve failure. (broken valve stem) etc.

Keep in mind if a cylinder is mounted in a tilted  position as seen on recreational vehicles the only way of safely filling these systems is using an 80% valve. Do not assume an attendant at a fill station will understand this. The attendant could overfill your system thinking it will shut off when filled!  monitor what is being done! It could be your vacation going up in smoke! or worse

Pressure Relief Valve. Prevents the contents of the cylinder from exceeding 350psig. And is unchanged from the old style valves.

In Conclusion, The new valve is absolutely functional and should not cause any undue problems as long as it functions normally. The valve function's (turns) easier  than an old style valve and this ease of operation is actually what leads to the most common problems associated with this valve,  Damage from over tightening. This can ruin a valve, as very little strength is needed to operate these valves. To prevent damage it is a good practice to turn the valve hand wheel one quarter turn clockwise after opening valve so that the next time we forget the valve in the "ON" position we will not damage it trying to open an already open valve


My number 1 test cylinder was refilled and in that process it was weighed, Cylinder weight = 17lbs, the weight prior to refill = 26lbs the scale was then set at 40lbs. This was 11lbs of Propane and 3 added lbs for fittings and hoses. The attendant stated the store policy is a flat rate for 20#’s=$17.00
10lbs cylinder=$10.00 (I was able to get away with that price, as we declared it a 10lbs cylinder) 5lbs Cylinder = $6.00.
The comment on the Blue Rhino site claiming only 17lbs of propane will activate the OPD float seems misleading.
Further more the old low flow problem complained about on many web site FAQ lists about OPD valves, [ roofers complained that there was not enough flow to]….., is most probably related to the 1st generation OPD valve, and that valve was in use before the standard 3 lobe hand wheel came into mandatory use. I think that problem has been put to rest. Amen!
AGAIN ADDED Aug 2018;
a reduced flow could be the result of a tripped excess floe valve or a tank adapter with an excess flow valve that delivers a lower BTU flow than the appliance requires.
Acme fittings will have excess flow where PLO fittings come with full flow or excess flow valves!
 

Click here to E-mail me

I alluded to the cylinder outlet fitting and the main shut off valve being the cause of most problem with propane devices. This chapter will explain the differences in Tank fittings and what we should expect of them.

In the above chapter there was discussion on a function called "Excess Flow".
We didn’t go to far into it as this is more commonly a function of the Tank fitting(s).

What is excess flow,
Any marked increase in the normal flow of a liquid or gas can be termed Excess, and is usually the result of a malfunction or failure of a delivery component. An example of a malfunction could be a free flow regulator.
An example of a component failure could be a broken hose or fitting.
When something like that happens an excess (much more) flow of vapor would be discharged into the surrounding air,or fuel the flame thereby setting up a very unsafe condition.
Prest-O-Lite fitting and Acme Brass Nut QCC fittings have been available for a long time that would sense this increase flow, and immediately shut or slow down the discharge of Gas Vapor.
Some of the early fitting set up this way would have to be manually reset after being activated, after the malfunction was corrected. The ones we see today are automatically reset by the use of a very small orifice in the valve witch is an integral part of the fitting.
A valve like this is also used in the Hydraulic industry and is called a "Velocity Fuse".
We will find Excess Flow fitting on most new Grills and Stoves that are used in recreation. They will be sized to meet this application. One for a small propane barbecue grill might be rated for 70,000btu, and that would mean enough vapor to accomplish this could leak and the device most likely wouldn’t know the difference, But if the appliance (Grill) is using most of this establish flow, and a leak occurred causing flow in excess of what would be consumed at 70,000btu there would be an imbalance in the sensor and the valve would close. The excess flow valve would stay closed until the appliance valve(s) are closed and enough time has elapsed for the vapor passing through the small orifice in the excess valve bring the pressure up to match the pressure on the cylinder side of the excess flow valve, or the malfunction corrected.
So if we have a setup like this,
1. Cylinder, 2. Excess flow POL fitting, 3. Regulator, 4. Delivery hose, 5. Appliance. We may never have a problem unless the pressure regulators free flow’s. This is a rare event, that could be caused by a fire or icing of the regulator, or its vent, but may not sense a failed delivery hose. The excess flow valve would have to be very closely matched to sense a leak downstream of a regulator, as a regulator is in its design a flow control devise on its own.
This is the setup that will cause us the most problem when we don’t understand what is happening.

1. Cylinder, 2. Excess flow POL fitting, 3. Delivery Hose (this was #4 in other setup), 4. Regulator 5. Appliance.
With this arrangement, the hose and regulator are in a different orientation and the length of the hose and the speed of opening the cylinder valve would dictate how problematic this could be.
I use this arrangement on 2 different appliances, 1st is a Weber Q portable Gas grill where I have a 20 lbs cylinder adapted, instead of using disposable cylinders (1lbs size), The 2nd is a Mr. Heater portable "Buddy" heater that I use in my fish house and I also have this adapted to a 20 lbs cylinder in favor of the 1 lbs throw away. Both of these adapters were purchased as per the manufacture recommendations.
This problem has such a simple solution that its almost nauseating, but if one isn’t aware of what is happening it could be terribly frustrating.
When the cylinder valve is opened, gas vapor is delivered through the excess flow valve, but because the delivery hose is empty, and depending on its length, an imbalance occurs each time this arrangement is assembled. Now if we were to just leave this device alone for a minuet, (unless there was a leak and this could just be a burner valve opened ever so slightly), the automatic reset function of the excess flow valve would reopen the valve. But what happens is when we don’t understand the mechanics of this we turn on our tank, and then open the burner valve and try and light the burner. By doing this we prevent the auto reset from functioning.
This can be remedied by simply waiting a short time after turning on the cylinder with the burner valve(s) in the off position until the delivery hose is charged by the orifice to match the cylinder side. And if your hearing is good one can easily hear the click of the excess flow valve upon closing and again upon opening.
Or, one could very slowly, open the cylinder valve. This is something that you will have to experiment with on your system and isn’t the best way to overcome this problem. The reason being, when you connect everything together, then make sure the burner valve(s) are off, and then open the cylinder valve we then know that it will take up to 1 minuet to reset the excess flow valve, and if this then doesn’t happen we most likely have a leak.
But,(don’t we love if’s and but’s)(and if they were mint’s and nut’s we could have a party). (In loving remembrance of Joseph Roots, RIP Joe)
BUT, if we elect to open our cylinder valve very slowly, thereby filling the delivery hose and as long as the leak wasn’t in excess of our excess flow valve, we could then light our burner with a relatively large gas vapor leak.
Remember, the excess flow valve isn’t all that smart. It can only see an imbalance of pressure on each side of it to activate. It doesn’t know why that is happening. That is our job.

In Conclusion,
The excess flow valve (velocity fuse) is a good thing to have in your system, but we need to understand how it works. We will see more problems with the excess flow Tank fittings when temps are high and tanks(cylinders are full, and valves are turned on too fast. We may get away with faster valve turning in cold seasons where it will cause trouble in the hot seasons.
 I have purchases 2 of these OEM conversion kits for the 2 above described appliance and I truly did not understand what they did, nor could I find any information on the internet to explain what they are and how they work in the way we do things in our day to day life.
I hope this will be of benefit to anyone who reads it, and if you are like me, you also may feel a tad foolish because its such an easy problem to over come.
Also keep in mind that every time we change the cylinder we must check for leaks. This is usually done with a soapy water solution like bubble soap. There are products available with a ethylene glycol base for cold weather use, or the high price electronic units the gas company might use. Just don't use a bic!
I will again remind everyone again that I am not an engineer, and this information was determined by un-scientific methods. Proceed with utmost caution at your own risk.

Click here for E-mail form