RE: re-circulation line

From: <Ed>
Date: Thu Oct 20 2005 - 09:19:00 EDT

Vijayan,

Your question is not a simple one and requires the outmost experience. You have to look at the equipment you are serving and the way your system is being controlled. I suppose recirculation line on a closed loop system can serve many purpose, but in this example I'm just focusing on Pump Protection.
Also in this example, the pump is serving several heat exchangers (heating or cooling).

Some items to consider :

1.) Under normal operating condition, fluid is transported to your Heat Exchangers thru your supply mains, out of the HEX and to your return mains back to the suction side of the pump.

2.) System #1 : At low load/demand, the system design parameters are maintained thru mixing or diverting control valves on your Heat Exchangers. What it means is that what's coming out of the pump comes back to the pump,
assuming no system leakage of course.

You don't need a Recirculation Line on this type of system.

3.) System #2 : At low load/demand, the system design parameters are maintained thru modulating control valves on your Heat Exchangers. What the control valve does is to control the amount of fluid going thru the HEX by partially opening/closing the valve port. This type of system is usually used where economy is a factor. What it does to the system at the worst scenario is that all the control valves can be fully closed and no fluid is going back to your return mains.

In this type of system control, you do need a recirculation line at the mains (with automatic valve). Because at the worst scenario, you will be dead heading the Centrifugal Pump.

4.) System #3 : At low load/demand, the system design parameters are maintained thru open/close control valves on your Heat Exchangers. This type of system is usually used where economy is a major factor. What it does to the system at the worst scenario is that all the control valves can be fully closed and no fluid is going back to your return mains.

In this type of system control, you do need a recirculation line at the mains (with automatic valve). Because at the worst scenario, you will be dead heading the Centrifugal Pump.

I hope this shed some light to your question.

Note : Placement of the By-pass/relief valve is worthy of discussion for

another day.

Ed Engalan

-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=pG6ZYQuC_Ytnz5bEkncZlyzOJRKmCirfAGFbTbH1HYDqsE6IKWD-8PrZoDZyPtxQsqRa3NyOXyLJ4rSqUq7875O7">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=pG6ZYQuC_Ytnz5bEkncZlyzOJRKmCirfAGFbTbH1HYDqsE6IKWD-8PrZoDZyPtxQsqRa3NyOXyLJ4rSqUq7875O7">PipingDesign@yahoogroups.com</a>] On Behalf Of VIJAYAN PULIKKATH
Sent: Wednesday, October 19, 2005 2:22 AM To: <a href="/group/PipingDesign/post?postID=ZkM_DagGZwxZ3UF6vKJqkqxgjQYKXJEG66pwQ4Avmdi_BDvq6QgXwySUhXDy34PyJzCNUr5INL2d4gpUbrpJuwJUkJwX">pipingdesign@yahoogroups.com</a> Subject: [PipingDesign] re-circulation line

Is it essential to provide a re-circulation line from the discharge side of a centrifugal pump to the suction side, in a closed loop system?

Any problem anticipated if recirculation line is not provided?

Request comments/advice from experts..

Vijayan Pulikkath
Asst Designer
Consultant Firm ,Chennai

---

  Yahoo! Music Unlimited - Access over 1 million songs. Try it free.

[Non-text portions of this message have been removed]

---

PipingOffice - Excel Spreadsheets for Piping Calculations <a href="http://www.pipingoffice.us/">http://www.pipingoffice.us/</a>

---

Main site: <a href="http://www.pipingdesign.com">http://www.pipingdesign.com</a>

Yahoo! Groups Links Received on Thu Oct 20 09:19:00 2005