×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Primary-Secondary Pumping Rule of Thumb

Primary-Secondary Pumping Rule of Thumb

Primary-Secondary Pumping Rule of Thumb

(OP)
A rule of thumb says that the location of the secondary pump in a primary-secondary piping arrangement shall always be in the supply piping of the secondary loop pumping away from the common pipe or decoupler, and the expansion tank shall be located in the return piping of the secondary loop upstream of the connection with the decoupler. What would happen if we connect the secondary pump in the return piping of the secondary loop, between the expansion tank and the connection to the decoupler, pumping into the decoupler?

RE: Primary-Secondary Pumping Rule of Thumb

A contractor did this to me in a congested boiler room, where the actual position of the pump ( although the construction drawings showed it correctly ) went unnoticed until certification. The system like yours was un pressurised and upon start up, a low pressure system was set up in the suction line of the secondary pump, causing noise due to air being released from the freshly treated water and no doubt in the long term cavitational problems with the pump impellor. I would also imagine that in long term there would also have been excessive air pockets formed in the radiation devices leading to circulation problems and a generally noisy system. Hope that answers your question.  

RE: Primary-Secondary Pumping Rule of Thumb

Carlos, it would defeat the purpose of having a 1° - 2° setup. The main purpose, as I understand it, is to allow the primary loop to pump known volumes to allow proper heat exchange, e.g., volume X with only B1 firing, volume Y with B1 and B2 firing, and volume z with B1, B2, and B3 firing.

If we place the secondary pump where you mention, what's to stop the secondary flow volume from driving through the primary loop? With that setup, why have a primary loop that maintains constant flow through heat exchange devices?

Basic application - a secondary loop pump often has a VSD to maintain a fixed loop differential (that way, the right flow and Cv can be anticipated through controlling devices). How will a 2° loop pump maintain that 2° loop DP when a disproportionate amount of its discharge volume might be driven through idle primary devices??

Chew on that a minute, then feed back. -CB

p.s., 1° = primary, 2° = secondary…

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources