Smart questions
Smart answers
Smart people
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • 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!

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

Donate Today!

Do you enjoy these
technical forums?
Donate Today! Click Here

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

lightecho (Mechanical)
13 Aug 09 9:09
I have a newer four story office building where the fire pump has not been set up as per 20 / A.14.2.7. I have noted this in inspection reports and the client has asked me to clarify. Currently the jockey pump is set to 100 / 130 and the fire pump is set to 85 / 95.

Fire pump specs out at 100 psi / 500 gpm with a 110.8 psi churn. Minimum static suction supply has been recorded at 60 psi with a maximum of 85 psi.

According to A.14.2.7 the settings should be:

Jockey pump stop: 110 + 60 =  170 psi

Jockey pump start: 170 – 10 = 160 psi

Fire Pump stop: 110 + 60 = 170 psi

Fire Pump start: 160 – 5 = 155 psi

The fire pump churn with max city supply would be in the 195 psi range. Presumably then, if the system is solid, system pressures would stay at about this pressure, with the weekly 10 minute runs.

This seems like a rather high 'normal' pressure. Am I missing something here / have my figures wrong? Due to the presence of a standpipe system, prv's or restriction devices would be required on the 2 ½" valves? Are there other implications I may be missing?

Thx

 

  
Helpful Member!  LCREP (Specifier/Regulator)
13 Aug 09 20:55
195 psi is too high and you need to reduce the pressure to below 175 psi OR make sure all sprinkler and standpipe components can take the pressure. If not this is a bigger problem. If the down stream components can take 195 then set it up as follows:

jockey on at 185 psi
jockey off at 195

fire pump on at 175 psi

You are correct on the PRV on the standpipe valves.


IF the system can not take 195 psi then


Jockey on at 162-3 psi
Jockey off at 172-3 psi

Fire pump on at 152-3 psi

****************************************
Fire Sprinklers Save Firefighters' Lives Too!


 

lightecho (Mechanical)
14 Aug 09 8:39
Thx LCREP

I've had to ask the original engineers about this before implementing any changes. I'm hoping I didn't put them in a spot.

Regards
D
FFP1 (Mechanical)
14 Aug 09 16:55
If the fire pump feeds automatic sprinklers, the maximum system pressure is limited to 175 psi. If this is the case, adjusting the activation settings will not resolve the problem. You will need to implement the suitable alterations to prevent pressures above 175 psi and then set the activation settings based on the "new" churn pressure.
lightecho (Mechanical)
14 Aug 09 17:41
FPP1      It is indeed a combined system. I am not seeing what you're getting at in regards to a 'new' churn pressure. The churn pressure will always be what it is for this fire pump, and this pump was spec'd for this system so short of redesigning the system, the churn pressure will not change. I'm hesitant to do ANYTHING at the moment if I can't set the pumps up as per 20/A.14.2.7.

The problem I see with LCREPs suggestion is the weekly churn tests are still mathematically going to push the system above the 175 psi mark.  
LCREP (Specifier/Regulator)
14 Aug 09 23:06
If you close the valve on the discharge side of the pump when u do your weekly churn test you will limit the amount of components subject to the high pressure. Is it perfect no, BUT it is better then subjecting the entire system to the higher pressure, yes. Is it the solution, nope.

The long term solution will cost $$$ and will take time to figure out. Run a hydraulic calculation to see if the 175 psi will still meet the hydraulic demands of the sprinkler and standpipe system. If so change out the components on the discharge side of the pump that can not be over 175 psi and install prv on each floor standpipe and sprinklers.

If not can you say variable speed pump and controller and BIG $$$.

As per NFPA 20 a relief valve is not permitted on the discharge side of the pump to reduce the pressure below system components rating. Remember the PRVS will need to be tested as per NFPA 25 every 5 years either on site or bench tested by the PRV mfg.

Like I said not easy, fast or cheap. Lets hope the water supply has improved since the original design of the system. I have been down this road way too many times, prepare to have fun!!

****************************************
Fire Sprinklers Save Firefighters' Lives Too!


 

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!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close