How to manage a broader range of pressure?
Volume 6/ Issue 3/ October 2019
The well-known Domestic Pumps from Xylem can handle up to 212ºF of boiling condensate, without cavitating, without vapor locking and in many cases even without elevating the tank. Units will do their job and transfer the condensate back to the boiler room, or to the boiler itself. The condensate will travel through pipes, fittings, ups and downs, before reaching its final destination. If it is a boiler feed pump then overcoming the operating pressure of the boiler should be accounted for, too. All the pipes and fittings along the way will try to give our pump a hard time because of the pressure drop along them.
To calculate this pressure drop you have to take into account how far you’re going, and how high you’re going. Sounds simple but it may not be. How far includes not only the distance but also the equivalent distance for each fitting, each valve, each elbow, and the losses for all the piping. How high refers to elevation, but elevation can be both positive and negative. This means careful review of plans, or specifications that have already taken all of this into account and determined what the total losses to the pump are in the discharge piping before the pump delivers its condensate to where it needs to be.
For low pressure boilers less than or equal to 50 psi the discharge pump pressure needs to be greater than the losses by a minimum of 5 psi. If losses are 10, we take 15. For systems where boiler pressures are greater than 50 psi, your discharge pump pressure needs to be greater than the losses by a minimum of 10 psi, in order to be on the safe side. If we run the unit under vacuum then another 5 psi should be added on top of the above rule, since the pump will be pumping out of an average of negative 5 psi. Sizing the pump is vital for proper operation.
Domestic Pump has standard solutions to overcome up to 100 psi of back pressure and this is more than enough for most steam heating applications.
But what happens when the pressure drop along the discharge piping is higher than 100 psi? Such applications can be found in industrial facilities or in larger steam heating systems with longer and more complex return piping. The solution to that is coming from our large Xylem family, and it is the Gould’s e-SV stainless steel multi-stage pumps. Utilizing the e-SV multi-stage delivers a great solution for high pressure condensate and boiler feed units with an efficient and easy-to-maintain multi-stage pump.
B&G Domestic Elevated Boiler Feed Units CMED
Here are just a few benefits from the synergy between Domestic Pump and e-SV:
• Pumps up to 500 psi discharge pressure
• Stainless steel multistage pumps
• Flexible pump solutions
Most importantly we make sure that the selected e-SV pump models will also transfer boiling water without cavitating and without the need to oversize them. This is achieved by selecting those models that meet the same required net positive suction head (NPSH) like the ones of the Domestic Pumps. All of our units are vented to the atmosphere. This means that the max. temperature of the condensate is 212ºF and it is a matter of atmospheric pressure and available water column at pump inlet to provide the required NPSH at pump inlet. We have taken care of that and the design of the units, including tank elevation and types of pumps, will meet the application requirements. Like with Domestic Pump, the e-SV models also have a low-NPSH version to transfer condensate with temperatures at the higher end.
Custom condensate return unit, model CED-e-SV
In addition to the standard pump options, like discharge pressure gauge, 60 or 50Hz applications, and motor enclosures, we can also add different pump discharge connection styles and different materials for the volute and seals.
Currently there is a number of standardized CMED-e-SV boiler feed models available. Customized units are always available for both Condensate Return and Boiler Feed Units utilizing a range of cylindrical and/or elevated receivers.
Please feel free to reach out with your custom unit inquiry and questions.
Check out our products on www.domesticpump.com
Bozhidar ‘Boz’ Ivanov
Sr. Product Specialist, Domestic Pump