QUESTION:
I recently purchased a used truck with a mechanical level gauge with an arrow indicating empty to full. I have never had a mechanical level gauge on a tank. Are those things good or should I replace it? In the past, I have always had sight bubbles on the rear head.
Ryan Bensinger
Rapid City, S.D.
ANSWER:
The purpose of any level gauge is to ensure the tank never fills so far that waste makes it through the primary, to the secondary, and lastly to the pump. At that point, pumping restrooms is an expensive game.
There are four types of level gauges used on vacuum tanks. As you mentioned, one of them is the sight glass. These are clear, bowl-shaped windows, installed in series of at least three from top to bottom on the rear head. The technician can glance at the bubbles and tell when the tank reaches capacity. This is a quick, easy way to determine if you have room for another load or if it’s time to dump.
Sight glasses are made of either plastic or glass. Generally they are secured by large thumbscrews, allowing for easy removal for cleaning or replacement. Bubbles get cloudy over time, and if they are not maintained, the driver cannot clearly see the level of waste.
SIGHT TUBE MAINTENENCE
Some PROs prefer a clear sight tube, typically installed on the back of the rear head. The tube fills and registers the same amount of waste as is in the tank. The sight tube must be strong enough to handle vacuum in the tank. A plain plastic hose will collapse, so something sturdier must be used. Usually there is a valve at the top and bottom of the sight tube, allowing for easy removal and replacement once the tube becomes cloudy.
A third tool for measuring tank contents is the electronic gauge. Electronic gauges are more expensive than fixed plastic or glass sight gauges, but offer additional features. An electronic gauge, installed inside the tank, uses a vertical rod with electronic sensors. Depending on the tank’s diameter and length, the gauge is calibrated to give a precise gallon measurement of contents. A digital readout inside the truck allows for constant monitoring of capacity.
The mechanical gauge you mention is popular with some PROs. This gauge is usually installed on the rear head. Inside the tank, an arm holding a 6-inch diameter stainless steel ball float moves up as the tank fills. Through simple gearing, the gauge on the outside of the tank registers empty to full.
All these gauges are currently in use on vacuum trucks. Each has a downside. The sight bubbles and the sight gauge need regular cleaning or replacement. The electronic gauge is expensive, and if something goes wrong with the gauge, it’s more difficult to repair and replace.
A buildup of waste can cause the float ball and arm on the mechanical gauge to stick, which may result in an inaccurate readout. PROs need to make sure the readout needle is able to move freely. If you doubt the accuracy of the mechanical gauge, look inside the tank and see if it needs cleaning.
PROTECT YOUR PUMP
Sight gauges protect your pump and help ensure that your truck isn’t running overweight. No matter which gauge you choose, it’s wise to make sure it’s in good working order and maintained as needed.
