Running a Long Horizontal Vent Line
Volume 7/ Issue 2/ April 2020
When we think of our Condensate Return Units the first one that comes to mind is our standard CC unit. As with any packaged unit, there are times when field conditions create a non-standard installation and operation environment. As a result, questions arise on what can be done. One scenario encountered involved a Model 306CC with a 36 gallon receiver. The location where this unit was installed required the vent pipe to run a horizontal distance of approximately 200-250 feet to reach an outside wall. “Will this be an issue?” is the question that must be answered. To provide the answer, we start by noting the “CC” series of Condensate units are rated for a maximum condensate temperature of 200°F. If the Overflow is piped and primed, the maximum is increased to 209°F. Next, it is important to ask a few additional questions about the installation to verify the “CC” is the correct Domestic Pump series choice. First question, “What is the expected condensate return temperature?” If above the “CC” maximum rating, the “CB” or “CBE” style should be considered. Regardless of final selection, a unit receiver, whether cast iron or steel, is not designed to act as a pressure vessel, and therefore must have proper venting. If the installation site has the potential to allow a condensate return temperature higher than 200°F (209°F), provisions must be made in the field to reduce it to, or below, the recommended maximum prior to entering the receiver. The receiver vent is sized to maintain atmospheric pressure conditions within the chamber at all times. If condensate at, or above, 212°F enters the receiver under this condition, “Flash” steam will develop, which can overtake the vent’s ability to maintain neutral pressurization, and thus lead to potential receiver or pump damage, and the discharge of live steam out the vent. The most common method of condensate cooling prior to the receiver inlet is the installation of a vented ASME rated flash tank, which can handle flash steam, allowing the removal of additional sensible and latent heat from the condensate, lowering its temperature to an acceptable level. Other suggested cooling methods include using a heat exchanger with external cooling source, or a dedicated cool water supply piped to the inlet pipe (or the receiver) with a temperature regulating valve to blend the two fluids for a mixed temperature below recommended maximum. While not recommended from Domestic Pump, as a last resort, we have seen the unit receiver oversized to increase the time between pumping cycles, allowing the condensate to cool. Our next question, “Where will the unit be located?”. With the request to run a 250’ vent line, this answer could reveal possible alternate solutions. If the unit will be isolated from pedestrian traffic, and in a location that does not have additional mechanical or electrical equipment, such as a crawl space, then venting right in the space may be an option, provided condensate temperature is controlled as discussed earlier. Another possible scenario may involve tapping into an existing vent line for other equipment, provided a thorough analysis is done to determine it is adequately sized to handle the equipment it already serves plus our unit, or that it is not subjected to any positive static pressure that can prevent the free flow of air from our unit, or possibly push harmful contaminants into our receiver.
When experiencing any kind of a horizontal run with the vent line, a 1” pitch is ideal (angled back towards the receiver) for every 20’ of pipe. So for a 250’ run, we need a total vertical height difference of 12.5” from the wall penetration back to the receiver vent elbow or tee. (NOTE: The elbow/tee will most likely be roughly 12” above the inlet threaded opening in the receiver, so looking for at least 24” of head space from top of receiver to wall penetration.)
In addition, with the distance to be traveled by the vent line, consideration to upsizing the pipe 1-2 sizes larger than our threaded vent connection size is recommended. This is due to resistance of air moving through the pipe. Over 250’, it is possible the air would run out of energy, and stall somewhere in the pipe before reaching the wall penetration. All the moisture in the air will condense inside the pipe, and no doubt cause corrosion. Overall, for proper instructions and recommendations on condensate units please reference our Domestic Pump Vented Condensates unit’s instruction manual and brochures on the Domestic pump website. There you will find more information about our units, and how to properly install them out on the field.