# Distribution Warehouse Mechanical Room



## dannyoung85 (Oct 8, 2013)

A job my guys are finishing up . It's the mechanical room for a new 375,000 sf cold storage distribution facility. Also a picture of one of the compressor skids for the refrigeration system serving one of the coolers.


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## MTDUNN (Oct 9, 2011)

Nice looking work. TM will have a review soon.

Only thing. Needs a hose hook!!!


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## dannyoung85 (Oct 8, 2013)

MTDUNN said:


> Nice looking work. TM will have a review soon. Only thing. Needs a hose hook!!!


 I agree on the hose hook however there wasn't one shown to be installed on the plumbing/piping plans.


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## TX MECH PLUMBER (May 27, 2011)

Great work. Are those prvs. ? 3 diff sizes ? Why ? That domestic feed to the building ?


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## dannyoung85 (Oct 8, 2013)

TX MECH PLUMBER said:


> Great work. Are those prvs. ? 3 diff sizes ? Why ? That domestic feed to the building ?


 This is the domestic water service entry. I asked the same question on the PRV's in the pressure reducing station. The engineer said that the large PRV on the bottom would handle the large pressure fluctuations and the middle one would handle the mid sized fluctuations leaving the small one to feather out the pressure. I'm still not sold on how it all works but the guys on site were joking that none of it mattered anyways because the owner would probably bypass the pressure reducing station all together via the butterfly on the top when they found out they have low water pressure at the far end of the building. The detail for this station is in the picture. I'm open to alternate descriptions as to how this thing works.


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## justme (Jul 4, 2012)

dannyoung85 said:


> This is the domestic water service entry. I asked the same question on the PRV's in the pressure reducing station. The engineer said that the large PRV on the bottom would handle the large pressure fluctuations and the middle one would handle the mid sized fluctuations leaving the small one to feather out the pressure. I'm still not sold on how it all works but the guys on site were joking that none of it mattered anyways because the owner would probably bypass the pressure reducing station all together via the butterfly on the top when they found out they have low water pressure at the far end of the building. The detail for this station is in the picture. I'm open to alternate descriptions as to how this thing works.



Talk about an OVER ENGINEERED system lol .


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## justme (Jul 4, 2012)

dannyoung85 said:


> A job my guys are finishing up . It's the mechanical room for a new 375,000 sf cold storage distribution facility. Also a picture of one of the compressor skids for the refrigeration system serving one of the coolers.


This wouldn't happen to be a USCS cold storage facility would it?


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## TX MECH PLUMBER (May 27, 2011)

dannyoung85 said:


> This is the domestic water service entry. I asked the same question on the PRV's in the pressure reducing station. The engineer said that the large PRV on the bottom would handle the large pressure fluctuations and the middle one would handle the mid sized fluctuations leaving the small one to feather out the pressure. I'm still not sold on how it all works but the guys on site were joking that none of it mattered anyways because the owner would probably bypass the pressure reducing station all together via the butterfly on the top when they found out they have low water pressure at the far end of the building. The detail for this station is in the picture. I'm open to alternate descriptions as to how this thing works.


It rite. It makes no sense. The top two prvs are pointless. Cuz the bottom will still maintain it outlet pressure. Pretty tho


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## dannyoung85 (Oct 8, 2013)

justme said:


> This wouldn't happen to be a USCS cold storage facility would it?


 No it's for a pharmaceutical manufacturer.


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## plumbing ninja (Jan 15, 2012)

Isn't it more a flow thing to reduce "hunting"! The smaller PRVs will be set with a 5psi diff from the next size etc! 
The water demand to process probably varies a bit depending how big the orders are for Viagra


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## love2surf927 (Dec 22, 2011)

plumbing ninja said:


> Isn't it more a flow thing to reduce "hunting"! The smaller PRVs will be set with a 5psi diff from the next size etc!
> The water demand to process probably varies a bit depending how big the orders are for Viagra


Could you explain this "hunting" a little more if you would.


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## dannyoung85 (Oct 8, 2013)

plumbing ninja said:


> Isn't it more a flow thing to reduce "hunting"! The smaller PRVs will be set with a 5psi diff from the next size etc! The water demand to process probably varies a bit depending how big the orders are for Viagra


 This does make sense now because I think the larger PRV is set at 80 psi on the outlet pressure and the middle one is set at 75 psi and the small one is at 70 psi.


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## iantheplumber (Sep 8, 2013)

seems like they should have all been piped the same size with the same prv's set to different outlet pressures to work properly...


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## wyrickmech (Mar 16, 2013)

iantheplumber said:


> seems like they should have all been piped the same size with the same prv's set to different outlet pressures to work properly...


the smaller one is more sensitive to lower flow conditions as the flow conditions increase larger prv,s are as accurate and needed. Most hospitals are set up with a high flow prv and a low flow prv so you can control pressure accurately under all loads. I really don't see why you would need a bypass though.


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## iantheplumber (Sep 8, 2013)

interesting...


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## iantheplumber (Sep 8, 2013)

still seems like the water would always just go through the one that allows the most flow...


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## iantheplumber (Sep 8, 2013)

or is it more just like a balancing act between the three to average out the outlet pressure?


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## TX MECH PLUMBER (May 27, 2011)

iantheplumber said:


> still seems like the water would always just go through the one that allows the most flow...


That's correct. If all three prvs are in service and the bypass is closed. No matter what volume is used on the building the pressure would always be whatever highest prv is set at. And the top two are useless It makes no sense. Unless. They want three options for pressure ranges and only use one prv at a time !!!!! Witch I don't see why they would want that. Volume and pressure are two diff things And if they only used the top prv. Think how much that would cut the volume


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## justme (Jul 4, 2012)

here's some info I found on why they want staged prvs of different sizes . Interesting article.

http://www.mehandeseng.com/aboutus_news_200408a.asp


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## iantheplumber (Sep 8, 2013)

TX MECH PLUMBER said:


> That's correct. If all three prvs are in service and the bypass is closed. No matter what volume is used on the building the pressure would always be whatever highest prv is set at. And the top two are useless It makes no sense. Unless. They want three options for pressure ranges and only use one prv at a time !!!!! Witch I don't see why they would want that. Volume and pressure are two diff things And if they only used the top prv. Think how much that would cut the volume



if they did want to use 3 different outlet pressures i would think they would want them all the same size..

the top one looks like half inch..


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## dannyoung85 (Oct 8, 2013)

The top one is 3/4".


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## iantheplumber (Sep 8, 2013)

what size is the water main after the prv's?


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## iantheplumber (Sep 8, 2013)

seems over engineered, the work looked good though..


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## wyrickmech (Mar 16, 2013)

iantheplumber said:


> if they did want to use 3 different outlet pressures i would think they would want them all the same size.. the top one looks like half inch..


the smallest prv would be the highest setting as the flow increased the pressure would drop then the next biggest prv would begin to function with a larger capacity and then if it could not hold the demand and the pressure dropped a little more the third prv would open. This way pressure is maintained at no more than the smallest prv,s pressure setting and no less than the largest prv,s setting


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## TX MECH PLUMBER (May 27, 2011)

wyrickmech said:


> the smallest prv would be the highest setting as the flow increased the pressure would drop then the next biggest prv would begin to function with a larger capacity and then if it could not hold the demand and the pressure dropped a little more the third prv would open. This way pressure is maintained at no more than the smallest prv,s pressure setting and no less than the largest prv,s setting


The end of this post contradicts its self. If the largest is say 80psi. Ur saying pressure will be no less then 80. And if the smallest is say 60psi. Ur saying pressure won't be over 60. The pressure would be bouncing back in forth. Unless I'm confused. About the post. 
I've seen/plumbed my share of mech rooms and have never seen this setup.


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## dannyoung85 (Oct 8, 2013)

I'll double check the PRV schedule when I go to work on Monday and see for sure what the outlet pressure on each PRV is and post a response. Maybe I should write an RFI to the engineer on this just for clarification lol.


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## TX MECH PLUMBER (May 27, 2011)

It be nice to know. Got me scratching my head on this one.


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## wyrickmech (Mar 16, 2013)

TX MECH PLUMBER said:


> The end of this post contradicts its self. If the largest is say 80psi. Ur saying pressure will be no less then 80. And if the smallest is say 60psi. Ur saying pressure won't be over 60. The pressure would be bouncing back in forth. Unless I'm confused. About the post. I've seen/plumbed my share of mech rooms and have never seen this setup.


what I meant to say was the water at a no flow condition would settle at the small prv.s setting at a high flow it would maintain at the low setting of the large prv


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## justme (Jul 4, 2012)

I guess no one read the article explaining why they do this.


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## TX MECH PLUMBER (May 27, 2011)

I did. Still trying to grasp it. It referred to drawings but I saw no drawings. That's how I learn In series to me means each prv would feed the next one. To gradually reduce pressure 
But what's in this thread still makes no sense


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## money turds (Oct 10, 2013)

Also wouldn't it have made more sense to install another rpz in parallel?
If you have to work on the only one on the incoming water service, the whole building is going to have to be shut down.


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## dannyoung85 (Oct 8, 2013)

Whenever I bid the job it came in over budget and the additional back flow preventer was value engineered out. So it was part of the job to begin with, the Owner just thought it wasn't worth the money.


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## TX MECH PLUMBER (May 27, 2011)

I'm still not getting this. The article doesn't match the pics in the thread. Il say it again. If all three prvs at in service. The outlet side of them will all have the same pressure and it will be the setting of the prv with the highest psi. The other two are useless. I don't see how volume would affect this operation Even more so that the smaller prvs have lower volume and pressure out puts. I don't like not understanding mechanical installs and principles in plumbing systems And I can't get this around my head It makes no sense


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## love2surf927 (Dec 22, 2011)

Ok I read the article and did a bit of research on how PRVs work. What I don't understand is the literature that was linked is speaking of pilot operated PRVs used with a direct acting spring loaded PRV which I understand however in the pictures these all appear to be direct acting spring loaded PRVs??? I understand the concept (I think) but, besides what I already mentioned I don't understand because I understand that water travels the path of least resistance so wouldn't the majority of flow be going through the bottom PRV in the pic since it has the largest diameter and is the most direct path. Two reasons I don't understand. Thanks tex for getting my mind going on this one, this is why I love our trade, complexities like this, even though I'm a struggling service guy.....


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## justme (Jul 4, 2012)

the largest prv is set to the highest pressure but as the flow or use of the line picks up the pressure drops which allows the 2nd prv to start flowing to help keep up with demand and if demand picks up to maximum then the pressure in the line will drop enough to allow the 3rd prv to start flowing. Now from my understanding is that the reason for these prv stations is because of the limitations of the larger prv's to keep up with the demand at full flow. So they set a 5 psi differential between each prv that will allow each valve to open up at a set point to help keep up with the demand of the facility without maxing out any of the prv's. Maybe our token engineer can explain further or I'll talk to a engineer buddy of mine and see what his opinion is on this.


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## justme (Jul 4, 2012)

I emailed him the pic of the prv station and I'll post back what he says about it.


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## TX MECH PLUMBER (May 27, 2011)

I see what ur saying but then why not have all prvs 2". How much volume can u really get from the top two. Even more so the top one


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## justme (Jul 4, 2012)

TX MECH PLUMBER said:


> I see what ur saying but then why not have all prvs 2". How much volume can u really get from the top two. Even more so the top one


That's a good question , I'm wondering if the smallest prv is supposed to be 80 psi , 2nd 75 psi and the 3rd 70 psi. To me that would make more sence with the fact the smallest prv would automatically handle the low flow demand and the 2nd and 3rd prv wouldn't kick until the demand required it and the pressure dropped. As soon as I hear back from my engineer buddy I'll let you know.


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## justme (Jul 4, 2012)

Here's a pic of what I think it should be in order to work, the pic of his print he posted calls out 10% for the smallest , 40% for the 2nd and 50% for the 3rd. In order for the smallest one to pick up the 10% low flow it would have to have the highest pressure setting in order to over come the 2 larger prvs below it , then when the demand picked up and pressure dropped below 75 psi the 2nd prv would kick in and so on.


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## plumbing ninja (Jan 15, 2012)

justme said:


> That's a good question , I'm wondering if the smallest prv is supposed to be 80 psi , 2nd 75 psi and the 3rd 70 psi. To me that would make more sence with the fact the smallest prv would automatically handle the low flow demand and the 2nd and 3rd prv wouldn't kick until the demand required it and the pressure dropped. As soon as I hear back from my engineer buddy I'll let you know.


Ignore my comment, it's been covered already


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## dannyoung85 (Oct 8, 2013)

justme said:


> Here's a pic of what I think it should be in order to work, the pic of his print he posted calls out 10% for the smallest , 40% for the 2nd and 50% for the 3rd. In order for the smallest one to pick up the 10% low flow it would have to have the highest pressure setting in order to over come the 2 larger prvs below it , then when the demand picked up and pressure dropped below 75 psi the 2nd prv would kick in and so on.


 See the picture of the detail that my guys built this reducing station off of. You are right on the flow percentages.


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## TX MECH PLUMBER (May 27, 2011)

Witch prv has the highest setting ???

The top one or the bottom one ?


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## wyrickmech (Mar 16, 2013)

TX MECH PLUMBER said:


> Witch prv has the highest setting ??? The top one or the bottom one ?


the last one I did they were set at 75-70-65


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## dannyoung85 (Oct 8, 2013)

The top one is set at 80 psi, the middle at 75 psi and the bottom one at 70 psi.


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## TX MECH PLUMBER (May 27, 2011)

Ok now maybe it's makes sense. Still strange tho. Does the facility really use that much water ?


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## dannyoung85 (Oct 8, 2013)

No I don't think they will use that much. The funny thing is that I was on site today and I noticed that the incoming water pressure was 56 psi so the pressure reducing station is serving no purpose. Unless they have us go back and install domestic water pumps as a change order, they may as well bypass the pressure reducing station. I'm anxious to see if they have water pressure problems once they go into production.


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## TX MECH PLUMBER (May 27, 2011)

Dam engineer. Didnt take pressure readings prior to design ?? Stupid. They are so smart ther stupid


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## justme (Jul 4, 2012)

dannyoung85 said:


> No I don't think they will use that much. The funny thing is that I was on site today and I noticed that the incoming water pressure was 56 psi so the pressure reducing station is serving no purpose. Unless they have us go back and install domestic water pumps as a change order, they may as well bypass the pressure reducing station. I'm anxious to see if they have water pressure problems once they go into production.


You gotta love that ****, we just got through installing a 4" prv at a cold storage facility per the engineer even though I told the guy the facility only had 55 psi . He said it was for if they had a pressure spike to over 75psi.


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## Plumberman (Jul 7, 2008)

justme said:


> You gotta love that ****, we just got through installing a 4" prv at a cold storage facility per the engineer even though I told the guy the facility only had 55 psi . He said it was for if they had a pressure spike to over 75psi.


I've only seen that much of a drastic spike in un metered fire mains here.

Usually we will step it down to factory set PSI on the suction side of the booster station and let it do its thing from there on out.


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## Plumb26 (May 18, 2013)

wyrickmech said:


> the smaller one is more sensitive to lower flow conditions as the flow conditions increase larger prv,s are as accurate and needed. Most hospitals are set up with a high flow prv and a low flow prv so you can control pressure accurately under all loads. I really don't see why you would need a bypass though.


I would only see the bypass used when servicing the valves. Just a guess.


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## Plumb26 (May 18, 2013)

So with low demand, the top prv is used. When the demand rises, pressure drops but volume is not affected (due to larger pipe size), then at full demand, pressure drops but never below minimum set pressure and volume is still unaffected. I think it'll work.:thumbup: 
And it looks awesome!


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## TX MECH PLUMBER (May 27, 2011)

justme said:


> You gotta love that ****, we just got through installing a 4" prv at a cold storage facility per the engineer even though I told the guy the facility only had 55 psi . He said it was for if they had a pressure spike to over 75psi.


Had an engineer do the same thing on a FAA control tower. He was from Houston. Goober he was


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## wyrickmech (Mar 16, 2013)

Plumb26 said:


> So with low demand, the top prv is used. When the demand rises, pressure drops but volume is not affected (due to larger pipe size), then at full demand, pressure drops but never below minimum set pressure and volume is still unaffected. I think it'll work.:thumbup: And it looks awesome!


yes that is exactly how it works the pressure drop is minimal just the difference between the high setting and the low maybe 10 psi at high flow


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