Wednesday, September 11, 2013

Steam Vents - Vent Rite

Arguably the most important, but neglected, component of a steam system, the air vent, comes in many shapes and sizes. Vent Rite valves are divided into four categories:
  1. Radiator vents – Models #1 & #11 
  2. Convector and Riser vents – Models #31 & #33 
  3. Main vents – Models #35, #75 & #77 
  4. Unit Heater vents – Model #57 
Walking up a hill burns more calories than walking on the flat. Add a 10 lb backpack and the rate of calorie consumption increases considerably. The same principle applies to a one pipe steam system. Much like the human body, a steam system is constantly breathing in and out. The expansion and contraction of the steam is the mechanism by which air is constantly expelled and drawn back into the system. Restrict those airways too much and the rate of breathing slows down to the point where the patient starts to burn more energy to perform the same task.

When the system is idle i.e. no call for heat, the system piping and radiators are full of air. Under standard conditions on a call for heat, water will change to steam when the temperature reaches 212°F and that water will expand at the rate 1:1760 i.e. 1 cubic foot of water becomes 1760 cubic feet of steam and travels through the piping as fast as 60 MPH. Unless that air can escape, the steam will begin to slow down and this halt in its forward momentum will be seen as an increase of pressure in the boiler. As the pressure increases, the pressuretrol which is there to protect the system will shut down the burner.

As the system cools, the steam will condense and flow back to the boiler. Meanwhile, the radiators remain cold as the trapped air prevented the steam from travelling to them. Now imagine those same radiators with holes (vents). The fast expanding steam pushes the air forward and out through the openings in the radiators. Obviously, the larger the hole, the faster the air will escape and allow the steam to enter and give up its heat. However, all steam systems are different and none have radiators exactly the same distance from the boiler. This means that the radiators nearest to the boiler may heat faster, satisfying the thermostat and leaving some of the radiators under heated. What to do?

Assuming that the steam boiler, piping and associated controls are in proper working order, the first step is to look at the main vents. In most cases, there will be one large, often neglected, vent located at the end of the main before the piping returns to the boiler. While this vent should be located 12” to 16” back from the elbow and mounted 6” above the main, many systems have the vent mounted on a TEE at the elbow. This location will cause premature failure of the main vent due to the accumulation of dirt and the effects of water hammer. For this reason, it is advisable to repipe the system at this location to accommodate the vent as detailed above. At the very least, elevate the vent using a 6” nipple.

A Vent Rite #35 is an ideal vent for this location. With an operating pressure of 3 psi, the #35 will ensure effective venting of the main thus allowing the steam to travel evenly throughout the distribution piping and on to the radiators.

On a smaller system with moderately sized radiators, a Vent Rite #11, which is a fixed opening radiator vent, is an excellent choice. Where radiators heat unevenly because of distance or mass, it is advisable to use the Vent Rite #1 which incorporates a dial to adjust the rate at which the radiator vents. This will permit balancing of the system assuming that each radiator has a #1 vent to adjust.

In use for over 70 years, the Vent Rite #1 is the original adjustable radiator vent, designed to replace a standard radiator vent. Today’s #1 has a dial with numbers which can be adjusted to increase or decrease the rate at which air is expelled from the radiator. With settings from 1 to 8, the Vent Rite #1 allows you to balance the system, thus allowing the radiators to heat uniformly.

Balancing the system takes some time and patience but is well worth the effort. The following is a suggested procedure for doing just this.

  • Set all #1 vents to highest number - 8 which represents the largest opening.
  • Start the system and observe rate at which radiators heat.
  • The fastest heating radiators should be dialed back first e.g. to 7.
  • Allow system to cool and repeat. 

The ultimate objective is to have all of the radiators heat uniformly with the vents set to the highest number for each respective radiator. It is conceivable that one radiator might be set to 3 while another is at 8. But usually it will be the farthest radiators that have the highest settings. Keep in mind that the largest radiators may also need higher settings to allow all of the air to escape.

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