PDA

View Full Version : Pressure Reducing Valve (PRV) for glycol system



Swags
06-20-2014, 12:48 PM
We are installing a system with a 2" supply and a pump that's capable of fairly high pressure. The 2" PRVs usually used for domestic water supply are $500 so and they only go down to 25 psi. I decided to buy several 1" PRVs, which are set to 12 psi, for each tank supply line. This seems like a safe solution to me, but I would appreciate any comments or red flags.

thanks

http://www.ebay.com/itm/Senninger-Pressure-Regulator-Valve-PSI-Reducer-PMR-PRL-/380264649480

NHBrewer23
06-20-2014, 08:19 PM
Rather than reducing pressure at each tank, why not just install a VFD controller on your glycol pump and control your supply pressure? Depending upon the number of tanks, a VFD would be a more affordable option with a decreased risk of mechanical failure or leaks.

Starcat
06-22-2014, 07:27 AM
This is not the correct approach and could invite several problems.
Why grossly oversize the pump?
There must be a bypass regulator installed and set correctly on the pump discharge line. This is convention which has been shown over time to be the way to manage the changing dynamics of the supply line. All modern package brewery chillers are set up in this manner.
There may be some possible merits to a VFD configuration on some systems, but a bypass regulator is still required and this is an extra layer of complexity and potential failure that in most cases is unnecessary.
One might be amazed at what can be run on a 2 inch line with a 1 HP pump. EG 645 BBL diversified load.
Also if you are using something like Goulds or similar you can install the pump with unions etc. in such a manner where a large pump of similar housing sequence can be swapped quickly. IN this case your power service to the unit needs to be considered for easy upgrade. Wire and breaker size, starter OL, etc.

gitchegumee
06-22-2014, 06:54 PM
Warren thanks for chiming in. I'd like to know exactly what is a bypass regulator? Pressure regulating valve? Pressure relief valve from supply to return? I do not recommend pressure regulating valves as this is just one more thing to fail. And when it does, it is NOT passive but will allow higher pressures in the jackets and risks damage. Could you please comment on my approach to this issue? I like a three-phase approach:
1) I select a pump that gives proper flow at low pressures. If needed, I trim the impeller to less than 1 bar possible pressure. I totally agree with you that 1hp and 2 inch lines permit great flow at relatively low pressures.
2) I use a bypass solenoid valve between glycol supply and return to open when all tanks' solenoids are off by stringing my NC contacts on my controllers together. This keeps the reservoir cold and uniformly mixed, but would tend to let my glycol header warm slightly and slowly if the glycol is not called for. (BTW, I use slow-closing solenoid valves--or better yet air-operated ball valves--for tank jackets)
3) I use a VFD to slow down my glycol pump to a preset half-speed rate when my bypass solenoid is active. This reduces pumping heat and saves energy, while keeping the system ready for cooling.
This seems to work for me and looks relatively fail-safe in a passive way. I've also been accused of overkill. Can you please let me know where you think I could do this different? Thanks!

Swags
06-23-2014, 11:35 AM
thanks for all the comments. there is a lot of brainpower on this forum.

I have a 1-1/2 HP pump that's rated for max flow of 20 gpm at 47 psi. I hope the pressure in the header is 15 psi or less. I plan to adjust a valve at the end of the supply header so the pressure is close to 15 psi. I could purchase a pump with less HP and greater flow if that's a better solution than using VFD. I believe the greater flow might be required sooner that later.

I was planning to use a VFD just for convenience of slowing the flow during times of low cooling demand. Will reducing pump speed and flow with the VFD also reduce the pressure in the supply header?

gitchegumee
06-23-2014, 06:20 PM
Plan on having the pressure at 15psi or less, don't just hope for it! I know that's not what you meant but seriously, brewers need to read and understand pump curves. It's one of those "stupid things every brewer should know" topics. Every brewer should know how reducing the speed affects the pump performance. How reducing the motor power, impeller diameter, and back pressure affect pump performance. What NPSH is and how to make sure you have what is required. And how to install a pump correctly with unions, isolation valves, instrumentation, and proper-sized, straight suction lines.
Now that I'm done with that pitch for engineering know-how, you will find that a larger diameter header will lower pressure and increase flow, all other things equal. Lower speed will dramatically decrease pressure too. And trimming your impeller will lower the potential maximum pressure in your system as well. I think your pump is built for more pressure than you want. What happens if somehow your pump's full pressure potential hits your tanks? Popped jackets/ruined beer/lost glycol? I know that you aren't "planning" to do that, but if someone accidentally shuts off your pressure regulating bypass? That's what I meant by having a passively fail safe system: one that could not possibly reach high pressures.
If you read the pump curve, you will see what your flow rate will be at your desired operating point: 15psi. Is this flow rate sufficient? Overkill? Might want to trim that impeller... Look at the pump curve again and follow the different impeller diameters to select a more favorable operating point. A VFD will help, but adds a layer of required complexity. I use one to simply reduce the flow during times of no required chilling--not required for safety. Reducing pump speed will lower your pressure considerably. You might want to look at your pump curve for a 1725rpm motor to see how so. If you send me your pump curve, or lacking that, your pump model and motor speed I can review it with you via PM.... Glycol systems are probably the most expensive and energy-intensive part of your brewery. It certainly pays to get it efficient and correct the first time. Good luck! Cheers!

Swags
06-24-2014, 12:18 PM
Thanks Phillip. Sounds like I own the wrong pump. I will send you the curve tables anyway but I probably need a suggestion for a new pump.

lhall
06-24-2014, 01:01 PM
Our glycol supply pump has a VFD that is tied to a pressure sensor in the outlet of the pump. It varies the speed of the pump to try to maintain the header pressure - slower when few tanks are calling for cooling, faster when more tanks are calling for cooling. There is a small valve connecting the supply and return loops for recirculation.

Your tank manufacturer can tell you the maximum pressure for the glycol jackets. 15 psi sounds a little low. The "15 psi" rating is for the tank itself, so as not to require ASME rating.

Bainbridge
06-24-2014, 01:27 PM
Our glycol supply pump has a VFD that is tied to a pressure sensor in the outlet of the pump. It varies the speed of the pump to try to maintain the header pressure - slower when few tanks are calling for cooling, faster when more tanks are calling for cooling. There is a small valve connecting the supply and return loops for recirculation.

Your tank manufacturer can tell you the maximum pressure for the glycol jackets. 15 psi sounds a little low. The "15 psi" rating is for the tank itself, so as not to require ASME rating.

Neat!

Ours just runs full bore (1.5hp, 2" main) and we throttle the valve on the return header to get the right pressure. Works like a treat. Though I have thought about retrofitting something like that above, to cut down on energy costs.

Starcat
06-29-2014, 02:47 PM
Phillip, sorry I am late getting back on this one.
Most of the Brewery oriented chillers such as Pro Refrigeration etc. have a bypass flow regulator on the machine such as a Watts 5300A that will bypass back to the well.
It runs from the discharge to the return side on the " Process " or " Plant " side of the loop and may be set where you want it to run 0-250 PSIG.
Although old school, this type of device is pretty reliable and provides failsafe as it will relieve at the pressure you have it set for.
http://www.watts.com/pages/_products_details.asp?pid=792
We happen to have a modular system with central well that I refitted with a new chiller, so I have one of those valves in the plant as well as 1 each on the packaged chillers.
Your Engineered System is much more elegant and I would emulate it if I had the proper budget.

It would be an honor to speak with you about pump dynamics at some point as this is not my strongest point.


Sincerely

paddy2123
04-11-2016, 12:40 PM
I just learned from a plumber about a Wilkins NR3 pressure reducing valve.
They run about $300 and are made of brass. The lower end pressure only are offered up to 1 inch.

http://www.airdelights.com/NR3_series.html

Can anyone comment if this type of valve is similar to the Watts and sufficient to protect the glycol system from over pressurizing.

yap
04-13-2016, 12:07 PM
not cheap, but not $500 and in the range you need...


http://www.mcmaster.com/#catalog/122/511/=11ysz92