The College and Career Readiness Center in Shepherdsville, KY visited our propane truck manufacturing facilities on October 25, 2011. Students learned about manufacturing and how to keep a clean, organized shop.

 
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Gallons Per Minute Pumped

Maurice Auxier

Over the past 50 years I have been involved in the propane gas industry, and I’ve heard many discussions involving propane pumps and the gallons per minute they will deliver. In the United States there are three basic pump manufacturers: Smith, Corken and Blackmer. Any one of these three companies is capable of delivering a reliable pump that will deliver the gallons per minute within the confined pressure allowed on a propane delivery truck.

Let’s start with the bypass, which by law limits us to a 125 psi differential pressure (differential pressure being the difference between tank pressure and allowed delivery pressure). There is a good reason for this. On a hot day when the temperature is hovering around 100 degrees, we are going to be dealing with a pump discharge pressure of around 325 pounds. To exceed this pressure would create a safety hazard as it would be creating more strain on hoses and other equipment that is not designed for this excessive pressure. Over the years I have found that most propane delivery trucks, built to handle home deliveries, will deliver between 50 and 65 gallons per minute. Once in a while we will see one that will deliver close to 72 gallons per minute. I have no answer for this as it is plumbed exactly the same way as an identical pump sitting beside it.

Looking Back at Earlier Gallons Per Minute

I remember back in the early 1950’s ,when I started in the retail gas business, I used to look forward to the annual Indiana Propane Gas Convention which was held in Indianapolis. We would sit around in our favorite supplier’s hospitality room and talk shop; sometimes until four in the morning. For the first two or three conventions that I attended, I would leave feeling a little depressed. It seemed as if I was not setting as many tanks or delivering as many gallons per minute/mile as some of the others. Now I admit, being from the Appalachian mountains of eastern Kentucky, I tend to be a little gullible. I’m not saying that any of my fellow “gassers” would lie, but they did tend to stretch the truth as the night continued and the drinks increased.

Various Hose Sizes

Can we manufacture a propane delivery truck that will give us more gallons per minute? The answer is yes, but most of the requirements for doing this are not practical (such as shortening the delivery hose or increasing the size of the hose). A 100 or 125-ft, 1-inch hose is preferred, but in most cases will not be long enough to reach all of the customers’ tank locations. Most of our propane industry customers order a 150-ft delivery hose on their new truck. We have built several 5,000 gallon units over the years that have been able to pump between 95 and 100 gallons per minute using a three-inch base-mounted pump which is connected to a three-inch meter by a three-inch pipe. In these applications, we used a 1-1/4-inch delivery hose. This works until the tank gets down to the 20 to 25 percent level, and then the pump starts to cavitate, which is caused by removing the liquid from the tank more quickly than it can replenish the vapor space. We would not have these problems if it was lawful to use a vapor return hose, but most states will not allow you to these in a metered delivery. Due to the limited amount of space under a vehicle today for emissions control, it would be difficult, if not impossible, to install a base mount pump.

Transports

Why don’t we have these problems with a transport delivery? Because we unload with a 2-inch hose, 15 to 20-ft long and use a 1-1/4-inch vapor return hose, which allows none or very little pressure buildup in the storage tank. This hose configuration will allow the transport driver to deliver somewhere between 225 and 250 gallons per minute. I have never heard a transport driver complain that his pump was not delivering enough gallons per minute.

Testing a Delivery Truck

A couple of years ago, I took one of our new BT&T delivery trucks and ran some pressure tests along the discharge piping system on the unit. We used a 3,000 or a 3,400 gallon unit for the test. I am not implying that this was a scientific test that would meet the requirements of the American Society of Mechanical Engineers, but I do think we gained some valuable information. We placed the first pressure gauge on the suction side of the pump, another one on the outlet of the pump, and one where the internal pump discharge line exited the tank on the back deck. We located gauges on both the inlet and outlet of the two- inch Neptune meter. The next gauge was located in the swivel on the hose reel inlet. The last one was located on the 90 degree shut off valve on the end of the delivery hose. We were surprised when we found very little pressure drop until we reached the hose and the 90 degree valve on the end of the delivery hose. We also found that the more hose you pulled off the reel, the less pressure drop you had. I had no way to measure the pressure drop through the double back check fill valve on the tank.

Examining the Options

As previously mentioned in this article, we are confined to only three or four options to increase our gallons per minute:

1. Use a shorter and larger diameter hose.

2. Increase the bypass pressure, which would be unlawful.

3. Use a larger double back check in the customer’s tank.

4. Use a vapor hose if allowed in your state.

On a residential delivery I think the time element involved connecting a vapor hose would offset any gains in gallons per minute. It might make us feel better, if we looked at it this way. If you had an open 55 gallon drum and you could fill it with propane in a minute or less, we probably would not be talking about increasing our gallons per minute. In the near future, I think we are going to have to be satisfied with the technology we have today.

- Maurice