FAQ: Watchdog Desiccant Breather

Why do I need this Watchdog Desiccant Breather? My reservoir already has a vent cap.

Most standard breather caps are intended to cover the filler opening on a tank or reservoir to keep out rain and large solid particles. Most of these are only capable of stopping particles of about 100 micron or larger. Studies have shown that to have a significant effect on abrasive wear, particles of 10 micron or less must be kept out of the system. Watchdog breathers remove particles of 2 micron and larger before they cause the silent destruction of your equipment. Most importantly, standard filler/breather caps do not remove airborne water vapor that causes chemical and physical changes resulting in loss of additive performance, sludge, bacteria growth, and corrosion. Watchdog breathers remove water vapor before it enters the tank or reservoir.


I do not see any water in my tank. Do I really need to pay for a Watchdog Desiccant Breather?

There are three states of water contamination in lubricants, hydraulic fluid, insulating oil, etc.:

  • DISOLVED WATER these molecules are dispersed one-by-one throughout the oil like humidity.
  • EMULSIFIED WATER these microscopic globules of water are suspended in the oil like fog.
  • FREE WATER settles to the bottom of the tank like rain.

All forms of water are generators of other contamination: rust, sludge, acids, soot, bacteria, varnish, and ice. All of these shorten the life of the oil or fluid, and the equipment serviced by it.

Why does the Watchdog Desiccant Breather cost so much? Am I getting value for my expense?

A major bearing manufacturer has stated that bearings can have an infinite life when small particles are removed from the lubricant. Hydraulic fluid will last three, even four times as long if water vapor is kept out of it. A power outage when a transformer fails is staggering. A Watchdog part number 39102 will hold up to a pint of water and will filter out 2 micron abrasive particles. The price of a breather is well below the cost of changing hydraulic fluid three times, or rebuilding a gearbox or cylinder, or having electrical shorting in a transformer.

There are several Watchdog Desiccant Breather part numbers, which size do I use?

The airflow BOTH IN AND OUT of the tank, reservoir, or gearbox determines the part number to choose. Two factors create airflow, they are: temperature variations (which cause very low airflow rates), and fluid volume changes caused by the stroking of hydraulic cylinders or by tanks being filled and emptied. The airflow rating for each part number is stated on the sales literature. We also state the equivalent fluid volume change, which a customer is more likely to know. The formula for the relationship between these two measurements is: 7.5 gpm (gallons per minute) of fluid volume change creates one (1) cfm (cubic feet per minute) of airflow.

Part numbers 39100, 39101, and 39102 are rated at 35 cfm airflow. This is the amount of airflow created by 260 gpm of fluid level change. At this airflow rate or fluid level change rate the pressure drop through these breathers will be approximately 1 psi. Pressure drop is an important concern because if there is too much pressure drop created by the resistance to airflow through the breather, the sides of the tank will be subjected to stress and could fracture, creating an implosion or explosion. Even though much larger volumes of airflow can pass through the breather (creating high psi drops), we rate all our models at the cmf that creates 1 psi, which is considered safe even for very thin walled tanks.

The pressure drop rating for a group of products is based on the size of the opening in the standpipe coming out of the bottom. Since Silica Gel adds very little to the airflow resistance, all part numbers with the same standpipe size are rated at the same airflow. Therefore 39100, 39101, and 39102 can be used for the same application, however, the tallest unit, the 39102 is the most economical because it has more life (more silica gel) for the cost.

Because the mounting hole on part numbers 39131, 39132, 39133, and 39134 is smaller (½” female NPT), they are rated for 10 cfm (75 gpm).

For larger airflow requirements the 39108, which has a 2″ standpipe opening, will handle 100 cfm (750 gpm).

How long does a Watchdog Desiccant Breather last?

The useful life of a breather is dependent on three variables. They are, in order of importance,

  1.  Frequency of Breathing
  2. Quantity of Silica Gel in the breather
  3. Ambient Humidity in the work area

Frequency of Breathing

Means how often does a new batch of wet air pass through the breather. Each time this happens water vapor is retained and the breather life is shortened. Examples of the extremes would be a storage tank that has fluid drawn out once a day; one load of water per day to be removed and retained in the breather = long life. A hydraulic cylinder strokes every 30 seconds; each time a new load of water to be removed and retained in the breather = short life.

Quantity of Silica Gel

The water holding capacity of a breather is directly proportional to the amount of silica gel in the breather. We have a chart that gives the maximum water capacity for each Watchdog part number. Our Cross Reference documents also show the comparison to various Des-Case models.

Ambient Humidity in the Work Area

Most users believe that the ambient humidity is the major factor in the life of breather; however, humidity works for us as well as against us; The amount of water a given volume of silica gel will hold is a function of the humidity; as the humidity increases the efficiency of the silica gel goes up, to approximately 40% of its own weight. Therefore as each load of wet air passes through the breather the air with higher humidity brings more water vapor to adsorb, but the silica gel can adsorb more at the higher humidity level. The end result is a small decrease in the life of the breather at higher work area humidity levels, but this is not as significant as the other two life factors. In certain environments, such as paper mills or areas with steam present, ambient has a more negative effect on the life of the breather.

After explaining these factors to a customer, they probably will still say, €œOK, how long will my breathers last?€. Most breathers in industrial applications will last 3 to 6 months, if sized properly. The first breather put on a tank or reservoir that has been in operation for a period of time will usually last a shorter time than subsequent breathers because it is having to dry air leaving the reservoir as well as coming in.

How do I know when the Watchdog Desiccant Breather has adsorbed all the water it can hold?

As the Watchdog® adsorbs water the silica gel turns from gold to very dark blue/green. In fact, it looks black to most people. Seeing a light green color throughout the gold is not a signal to replace the breather. When all of the silica gel has changed color, to the very dark blue/green, the breather should be replaced. A breather that still has a small amount of gold color, or even light green color, showing is just as good as a new breather.

Can the filter cloth become clogged in the Watchdog Desiccant Breather?

In a typical industrial application, it is unlikely that the 2-micron filter cloth will become clogged before the breather has reached its full capacity of water. The filter cloth is a patented knit polyester with the two sides made differently. The side that is placed in the up position in the breather is knitted with a loose pile surface that closes to 2-micron when hit by the incoming air. When air is expelled from the tank it goes back through the filter and the knit opens back up (loose) throwing off the particles collected on the top surface. In the filter industry this is called “€œbackflushing€.” These particles flow out of the breather with the expelled air creating a “€œself-cleaning”€ process.

How do I dispose of a used Watchdog Desiccant Breather?

Watchdog® breathers are manufactured with all materials that can be disposed of as solid waste as defined by local regulations. However, if a breather is used on a tank that contains regulated fluids, the breather must be disposed of in the same manner as required for the fluids.

Can I wash equipment that the Watchdog Desiccant Breather is installed on?

Yes. Water will not enter the breather unless you spray water directly upwards into the top cap of the Watchdog® breather. They are designed so that water cannot enter the breather under normal conditions. Unlike competitive breathers, normal splashing of fluids will not enter the breather. Washing equipment is safe and will not reduce the breather life.

Will the Watchdog Desiccant Breather break if I drop it?

It is possible, but not likely. Our breathers are made of rugged ABS plastic caps and a high impact resistant acrylic tube, adhesively welded together. While they are sturdy enough to withstand most environments, the acrylic tube can crack if dropped from significant height onto a shop floor. If the tube cracks or breaks, solid particles and water can enter the breather through the crack. It is best to replace any breather that is cracked or broken.

Can I replace the silica gel myself one it has changed color? Or can the silica gel be dried and reused in the Watchdog Desiccant Breather?

The Watchdog® breathers are designed so you cannot remove the top or bottom cap without breaking the breather. This is a safety precaution to keep silica gel beads from spilling and to assure that particles and water vapor cannot enter the unit except where required.

Why are so many adapters available for the Watchdog Desiccant Breathers?

The wide variety of applications for breathers requires us to make installation for our distributors and customers as easy as possible.

Can a Watchdog Desiccant Breather be mounted in any position, vertical, horizontal, or on an angle?

Breathers should be mounted in the vertical position, or at least no more than a 45º angle. Even though the Watchdog® Breathers are vibrated during assembly to assure maximum filling, the silica gel settles during shipping, creating an air passage above it when the unit is in the horizontal position. Air, like people, takes the path of least resistance, and in this case it would miss the silica gel and would enter the tank undried.

Must a Watchdog Desiccant Breather be mounted on the tank/reservoir or can ti be mounted remote?

In many applications it is desirable to mount the breather away from the tank for better visibility or better access for changing the units. Remote mounting can be accomplished using tubing or pipes for the air to flow from the breather to the tank. Care must be taken to insure that there is no airflow obstruction in the line and that there are no air leaks after the clean dry air has left the breather. Piping can also be used to achieve a vertical mounting position for the breather where space limitations exist on the tank or reservoir.

I have a down stream filter already. Do I need this and a Watchdog Desiccant Breather?

Harmful contaminants, both abrasive particles and water, enter an enclosed system from three sources:

  • Built In: this is debris from manufacturing and service of the equipment. It includes dirt and dust, burrs, contaminated fluids, etc.
  • Generated: such as mechanical wear, additive precipitation, hose fibers, etc.
  • Ingested: which enters the tank or reservoir from the atmosphere. The breather prevents the ingested material from entering the tank and causing harm to the fluids and the equipment. The down stream filter removes contaminants that are already in the system before they do additional harm.

Can I use my Watchdog Desiccant Breather outdoors in cold or hot conditions?

Yes, Watchdog Desiccant Breathers are designed for use in temperatures ranging from -20ºF to 200ºF.