First time CNG fueling episode - didn't go smoothly

[snewman24]

OK, so I've been putting off fueling up my 2004 Express van that I bought at auction from GSA. It's been sitting in the driveway and I was afraid it wouldn't run on CNG or have a leak so I've been procrastinating. Finally went down today after watching several CNG fueling videos on the internet. All the videos make it look really easy. Well, I get down there and firstly, the fueling handle/coupler doesn't look anything like the videos. It has a spring-loaded coupler and a squeeze handle like a gasoline pump. The coupler wouldn't snap on until I squeezed the handle then finally snapped on. Scanned the credit card, lifted the handle, and the pump just sat there showing $0.00 - wouldn't fill. So the attendant told me to void the sale and move up to a different pump in front of the station and he would come out and show me how. Finally got the 2nd pump to start filling but it didn't just smoothly fill it. It was on & off, on & off, screeching for several seconds, then less screeching, then off...repeating over & over. He says this is normal. Finally reaches 100% filled. Then he showed me the little lever with a yellow arrow that needs to be flipped, and the nozzle automatically pops off the fill receptacle. Quite the experience - I felt like a little kid on his first day at school

Oh, BTW, the van runs fine on CNG, can't really tell the difference....

[Highmarker]

Congrats snewman24!

Actually pumping CNG is much safer than gasoline. The CNG refueling system is a "closed" system. It will not allow you to dispense CNG into the open air like gasoline pumps do. If you do not have the fueling nozzle properly attached to the vehicle, the system will not dispense the gas.

I personally have not used the "gasoline-like" pumps, but I've been told they are really slick to use.

[snewman24]

The fill nozzle looked this this one:

http://www.weh.us/products/refuellin...tk17-cng.en-us

[BobBaldwin]

Congratulations!! I had to have some assistance the first time I fueled as well.

[wagnewvt]

I needed the station attendant to show me how the first time also.

[John Mitton]

Highmarker, the WEH gasoline-like fill connectors are in use at the Salt Lake City L-CNG station off 21st south if you want to try one. Pretty slick.
2025 South 900 West. Salt Lake City, UT84104

[oxjeremy]

I would say that a good majority of people felt like idiots when they first tried to fill their CNG vehicles...I think that I have used maybe 4 different styles of nozzles. The ones on the link I like the best though...seems to attach and detach the easiest.

[wagnewvt]

I think it would be pretty cool to have one of those TK-17s on a Phill!

[BobBaldwin]

I think it would be pretty cool to have one of those TK-17s on a Phill!

I am sure WEH would sell you one! The U.S. rep lives right here in Katy, TX with me.

[Robert_Stiles]

Finally got the 2nd pump to start filling but it didn't just smoothly fill it. It was on & off, on & off, screeching for several seconds, then less screeching, then off...repeating over & over. He says this is normal. Finally reaches 100% filled. T.

Just to explain"why" the dispenser did what it did. CNG dispensers are programmed to determine the volume of the cylinder to be filled so that it does not over pressurize the cylinder. To do this several factors that must be taken into account before filling can begin. 1) what is the total volume of the cylinder(s) to be filled. 2) what is the ambient temperature. (I will explain why this important in a moment). 3) what is the current pressure level in the cylinder(s) to be filled To get this information the dispenser will then do the following:

1) When the fill nozzle is connected to the vehicle the dispenser is able to take an initial pressure reading
2) the dispenser will dispense a measured amount of gas into the cylinder then shut down
3) It will wait for a moment then it will take another pressure reading - at this point the dispenser is able to calculate an approximate cylinder volume and will begin to fill with another measured amount of gas... It will again stop
4) during this pause it is taking another pressure and temperature reading. Based on this data the dispenser will have an accurate idea of the installed cylinder(s) capacity on the vehicle being filled.
5) The dispenser will restart and continue to fill another measured of gas and again stop to take readings.
6) It will continue to do this until it senses that the cylinder has reached equilibrium with the storage (i.e. 3000 or 3600 psi depending on the vehicle and the station.

As I mentioned temperature is a very critical factor when filling a CNG vehicle. Gas pressure changes as the ambient pressure changes and will also change as the vehicle is being filled. First it must be stated that gas is measured at what we call "standard conditions" those conditions are that the gas must be at 70 degrees F @ either 3000 psi or 3600 psi. As the temperature varies from that 70 degree norm it effects the pressure. the "rule of thumb" here is that for every 10 degrees you vary the temperature you change the pressure by 100 psi.
You want a full fill (i.e. 3000 psi or 3600 psi ) so as an example you are filling at a time when the temperature is 50 degrees (i.e. 20 degrees less than 70) that means that the pressure in the tank will read 200 psi less on the gauge. (the dispenser is calibrated to take this into account) so if the gas warms to 70 degrees F you will recover that 200 psi. The other item a dispenser must take into account is the "heat of compression" If you were to measure the temperature of your cylinder prior to fill then again after you have filled you will note an increase in the temperature. The dispenser must also take into account this variable and stop the flow of gas so as not to give you a false fill reading. At the end of the filling process and you were to look at a pressure gauge again depending on the temperature you might read either a little less or more than your vehicles rated pressure. We then go to what we call "settled pressure" That is when the cylinder is returned to "standard conditions" and at the point you should have a "full fill"

This was a very windy explanation as to why the filling process was " on and off and on and off" and the attendant told you it was normal... He was 100% correct..... Hope this helps you understand the process a little better