HEADINGLY, Man. – Steadily increasing nitrogen prices are making it more important than ever that farmers who want to save on input costs have next year’s fertilizer delivered the fall before.
That need has caused more large vertical tanks to pop up across the Prairies.
According to Chris Thompson at Polywest, the largest polyethylene tank distributor in Western Canada, portable twin and triple 3,000 gallon polyethylene tank trailers are rapidly becoming more popular.
“We’ve been selling the 3,000 gallon poly tanks on a double trailer since 1997. Six years ago, we had Schaben Industries design and build the 9,000 gallon triple unit for us. In that time, we’ve sold as many of the 9,000 gallon triple trailers as 6,000 gallon double trailers,” he said.
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Thompson said dual-purpose tank trailers allow a producer to store liquid fertilizer in the yard over winter. In the spring, the trailers can be placed where needed, but they are designed to haul only empty tanks.
He said portable tank trailers sold in Western Canada are used for liquid fertilizer, and some see extra duty serving as water tanks at spraying time. The same 3,000 gallon tanks are used in both double and triple configurations.
He said the 9,000 gallon unit works well for Canadian farmers because they can fill all three tanks from a super-B tanker.
This type of high-capacity, vertical poly tank has been available from Schaben Industries in Nebraska and J. Skiles in Kansas for about 25 years, he said.
In that time, manufacturers have learned that polyethylene shrinks two to three percent at the end of the moulding process, making it almost impossible to mould in an accurate thread.
“When you’re holding that kind of liquid volume, the thread must be perfect in all temperatures. It must be a specified taper that meets national standards. With polyethylene, you cannot control the shrinkage and you cannot be sure it will seal consistently.”
Thompson said a tap and die threading operation doesn’t solve the problem.
“On the female end of a moulded poly fitting, you can tap out the tube and cut in a new thread. The male fitting can have new threads cut with a die. But polyethylene expands and contracts with temperature changes, so you loose the seal. It’s too pliable to hold a good seal.”
Thompson said Polywest only sells tanks with a bolt-in threaded bulkhead for the valve. The company simply does not trust moulded-in threads because there is too much at stake should a leak occur.
Each 3,000 gallon tank holds about 37,000 pounds of liquid nitrogen. He said that’s too much head trying to get out the bottom and too many dollars of liquid to risk with a moulded-in bulkhead.
“It’s a lot of fertilizer to dump in one spot if you don’t catch it on time,” he said.
“And accidents can always happen. With a double or triple portable, you pull to your spot then release the valve on the hydraulics to set the trailer down.”
With three inch plumbing, the valve sits about six inches off the ground. If the operator is in a hurry and fails to check for rocks or a high ridge in the middle of a field road, the valve could be knocked off.
Or if the trailer is parked properly, but is on soft ground, it could settle and snap the valve during a heavy rain.
“It’s still a disaster if you have a bolt-in bulkhead, but it can be a bigger deal if you have a molded-in bulkhead.”
Thompson said the flange on the bolt-in bulkhead is wide enough to spread any accidental force out over a larger area, compared to a moulded unit.
“The beauty of any poly tank, whether it’s moulded threads or a bolt-in design, is that it’s usually repairable. Polyethylene is a very forgiving material. If you really torque it and ruin it, poly doesn’t send cracks running up the side of the tank. The crack only extends far enough to dissipate the force, typically not very far.
“If you should happen to damage a tank with moulded threads, there’s a possibility you can salvage it. You buy the regular $10 bolt-in bulkhead and carefully cut out the hole so it fits. It’s do-able. We’ve done it.”
He concedes there are advantages to a moulded-in fitting. The operator gets a smooth flow out the bottom of the tank, so cleanout is easier. He says that’s good in a smaller volume, cone-bottom tank where there’s less down pressure from the liquid. But it’s a different scenario when there’s a lot of product in the tank.
Thompson said the company’s standard inner flange component sits ¾ of an inch high, preventing a small amount of liquid from draining.
“We get a ring of liquid about an inch wide and three-quarters of an inch deep. Diameter of the ring is nine inches, so the total is a couple cups of liquid. In a 3,000 gallon tank, it’s not significant.”
Whether a farmer is switching from fertilizer to straight water or vice versa, it’s not likely a small amount of residue would matter. But for those who want absolute cleanout, Polywest has a $10 solution.
“We have a total drainage bulkhead flange for the inside of the tank. The bolts go through raised legs so every drop of liquid runs out the bottom. There is no dam in there holding back the liquid.”
Like the company’s regular bulkhead, it uses all stainless steel hardware and is made of a high-density material called glass-filled polypropylene. This material is designed to be machined and threaded to the close tolerances required to meet national pipe thread standards.
All bulkhead flanges that go inside are manufactured with threaded female fittings to allow installation of an anti-vortex fitting.
“When that mass of liquid starts turning, you get a vortex at the bottom of the cone, so the tank drains slower. The vortex sucks air into the line. It throws off your meter and gives you wrong readings. With enough air in the line, especially on the three-inch systems, you can loose the prime on your pump.
“But with a molded-in bulkhead, there are no internal threads to allow for installation of a vortex fitting.”
Thompson said all Polywest polyethylene tanks have a UV stabilizer incorporated into the resin to resist deterioration from sunlight. The triple 9,000 gallon unit with trailer sells for $9,000.
For more information, contact Chris Thompson at 204-924-8265 or visit www.polywest.ca.
