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Floats - What, When, Where

by Doug Pushard

Picture of floatFloats are the most common and simplest way to control or monitor a rainwater, greywater or blackwater system. They can be thought of as a simple on/off switch, but can do much, much more. Floats are a closed ball with an electrical wire attached. Inside the ball is simply an electrical contact. Floats are typically tethered to something in a tank (i.e. the pump or a pole).

These devices float on the fluid in the tank. If there is no liquid, they hang as pictured (i.e. this is typically referred to as float down) If there is liquid in the tank than this device would float on top of the liquid (i.e. referred to as float up).

Floats come in two types – type 1 - ON WHEN UP or type 2 - OFF WHEN DOWN. This is critical to remember when purchasing and installing a float. The wrong type will do the exact opposite of what you want it to do. Type 1 - ON WHEN UP floats are used to empty (i.e. PUMP DOWN) a tank. Rainwater, greywater or blackwater systems will use this type of float to ensure the tank does not overflow.

PUMP DOWN or Normally Open (NO) is the most typical and widely available float type. In this configuration, the float is ON in the up position. An easy way to remember this is PUMP DOWN empties the tank. Type 2 - ON WHEN DOWN floats are used to fill (i.e. PUMP UP) a tank. Rainwater, greywater or blackwater systems will use floats of this type to add water to a tank to make sure it is never empty.

PUMP UP or Normally Closed (NC) configuration the float is ON when the float is in the down position. An easy way to remember this is PUMP UP fills a tank. This type of float configuration is used to fill a tank to a certain water level and then shut if off when the float rises to the specified level (i.e. where is has been connected to the pump or pole).

Although floats have two wires, they do not utilize a complete electrical current* (i.e. load and common); instead only using one leg: common. One of the wires of the float will be connected to common (I.e. incoming current) when the float is in the proper position this common is carried through the other electrical wire (i.e. outgoing current) to complete a circuit. Floats complete a circuit just like a single pole light switch.

For example, many sump pumps (e.g. basement drain pumps) come with a pre-attached float. When the float is up, the pump comes on and as the float falls down the pump goes off. The pump is wired to the load side of the electrical current and the float provides the on/off switch through the common side of the current. The intent of the float in this case is two-fold: 1) to make sure the pump gets electricity when there is water and 2) makes sure the pump does not run when there is no water. This latter case prevents the costly burn out of the pump from running dry. The float is the only control device for the pump.

Floats are labeled (i.e. Pump UP or Pump DOWN). If the labeling is not clear, test the float at the store to make sure it is the right one. Save yourself time and aggravation by preventing the simple mistake we all make at least once.

When connecting the float onto the pump or pole, remember the float does not turn on until it is the full UP position or the full DOWN position depending on the float type. Make sure there are no obstructions that will prevent the float from reaching this position. Common mistakes include positioning the float too high and it hits the ceiling of the tank prior to being all the way up or connecting it too low on the pump so it rests on the bottom of the tank prior to hanging all the way down. Both of these will prevent the float from doing it’s intended job.

In looking again at the picture at the start of the article, there are two floats pictured. In this case, the lower float turns on a make-up water line valve (i.e. on when down) to keep the tank filled to a minimum level. The upper float turns on a valve to allow the tank to pump water (i.e. on when up) to an above ground tank. These floats work together to keep some water in the tank at all times as well as make sure the tank does not overflow.

Floats also come in two different electrical configurations: a standard three Picture of float plugsprong electrical plug or just two bare wires. In the case of a float with a plug on the end, the float plugs into the wall and the pump or the device being controlled plugs into the back of it (see picture). As outlined above, even though the float looks to have a standard electrical outlet plug on it’s end, the float wires only carries one line of the electricity.

In the two-wire configuration, one wire is connected to the common (i.e. generally the white wire) wire and the other end is connected to the common wire of the device being controlled (e.g. the pump). Never wire these devices near water or when plugged in. A professional electrician is recommended and, in many jurisdictions, required to wire water systems. Please check with your local code officials.

The most frequent ways of using a single float is to connect it to a pump to make sure it does not come on when there is no water in the tank (i.e. PUMP DOWN) or connect it to a valve to fill the tank to ensure it is never empty (i.e. PUMP UP). However, floats can be used for many, many other purposes. Floats are part of almost every rainwater, greywater or blackwater system. They provide a very reliable way of controlling the behavior of the system.

Part II of this article will cover other ways floats can be used to automate the ongoing routines of these water systems to lessen the maintenance load.





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