Know Your Payload

Know your payload and it will go a long way to help understand the true weight allowance on your truck and what the debris actually weighs. You can confidently tell your customers what you are hauling, not what you think you are hauling.

Many times over the years I have been on site working with other trucks and heard someone say, “I’m full, I have 12yrds on.” To which I reply, “Isn’t that a 12 yard tank?” Their reply, “Yup. I’m full to the rim, so I have 12 yards on!” So, technically yes, you are full. But, in most cases you don’t have on as much as you think you do!

Here’s why and it’s simple. Today, most Hydrovac manufacturers equip their trucks with some form of “shut-off” system that will prevent you from overfilling the tank. This system is usually a float ball style shut off that will float up with rising water and plug off the suction pipe in the top of the tank. Thus, stopping the airflow to the blower and preventing you from contaminating the cyclone, filter and ultimately the blower itself.

These systems consist of a “cage” that contains the ball hanging down from the top of the tank. This system will prevent the use of approximately the top 1.5 – 2ft of tank space. This of course, determines HOW MUCH material you can fit into the tank! Because of this design, you will never fill your truck to its maximum capacity.

Outside factors like the force of the vacuum, angle of the truck and even the rocking/movement of the truck will determine when that float ball gets sucked up into the shut-off. Once that happens, you are full folks!

In most of the manufacturers designs, you will lose 1-2 yards (or meters) of the tank capacity stated in their specifications. Many manufacturers will state total tank capacity as well as “useable” tank capacity in their specifications so please keep an eye out for this.

All of this adds up to the fact that when your 12 yard tank is full, you will only have 10.5 to 11 yards of actual debris inside. A midsize unit tank of 10 yards might only hold 8.5 or a maximum of 9 yards. A smaller unit with a maximum capacity of say 7 yards (or meters) will probably only have 5.5 to 6 yards inside.

Knowing this will go a long way to help understand the true weight allowance on your truck and what your debris actually weighs. Want to know what your truck actually hauls? I’m sure there are many ways to determine but, here is a simple formula that I have used in the past.

NOTE: this is done in yards and doing the conversion to cubic meters will require a different mathematical formula as the amounts of material are different.

1. Make sure your debris tank is completely clean and scale your truck to determine an “empty” weight. Then, find a source of open water that you can LEGALLY draw from. We recommend that you contact your State, Province, County or Municipality to be sure you have permission to do this.
2. Engage your blower and load your unit until the vacuum stops. For example, the float ball floats up and stops the suction.
3. Make sure you only use FRESH water for this scenario because the weight of Produced Water or Salt water will be different.
4. Head back to the same scale you used before so that you can be sure of a consistent measurement. Many scales will differ and even a few percent can make a difference!
5. Now, let’s do some math. A cubic yard of FRESH water weighs 1683.85 lbs. Take the difference in weight between full and empty then divide that number with the 1683.85lbs that we know constitutes one cubic yard.

BAM! The number you get is your tanks useable yard amount. Easy!

Now that you know what your truck actually carries in yards, you can confidently tell your customers what you are hauling and not what you think you are hauling.

If you ever need help with this, please feel free to contact me at any time. I’d be glad to help!

Tanks and dig on!

–Terry Rawn