Pressure switch

[amin36]

Hi guys

I am working to make a Continuous flocculation system for one of the pools i am controling.here is the referance:

Pool Water Treatment Advisory Group - Polyaluminium Chloride PAC Dosing

www.cpc-chemicals.co.uk

As you can see one of the things i have to consider is a pressure switch:

pressure switch should be fitted post filter and set to operate when filter pumps go down of any reason

I need to know what type of pressure switch are they excactly refering to?can anybody tell me please?

Ps;i know that TFP usually does not recomand flocculation so that is just my personal question.i do not mean to violate the laws here

Thanks

 

[Bama Rambler]

They're looking for a pressure switch that will shut down the floc system when it senses lower than normal pressure in the line after the filters. Basically just a normally open switch. You need to look for an adjustable pressure switch that covers the range of pressures normally seen by your filter discharge.

 

[setsailsoon]

Amin,

Thanks for acknowledging TFP guidance to avoid floc in pools. I have a lot of experience with it for industrial applications and it works well where the design accommodates it. Pools just aren't built that way. I'm not trying to debate that but I would respectfully ask you to think about the design. Floc works by having good mixing with the water and then a fairly long period in still water where particles agglomerate and become heavy enough to settle where they can drop to the bottom with time determined by Stokes settling velocities. This usually take hours. After that water is drawn off the bottom and disposed of so most of the floc is removed from the system. Even with these designs circulation filters plug often for several days just from residual floc that's not removed. Your design looks like the floc is introduced just before the filter which is only going to plug up the filter pretty quickly unless there's some kind of very special filter and floc material that behaves totally different from the traditional I'm familiar with.

Just trying to help not criticize and good luck to you!

Chris

 

[amin36]

Thanks
Bama Rambler

Any specific brand you recomand?
Could you give me a link?

 

[amin36]

setsailsoon
Thanks chris

First of all let me mention that the substance being used here is poly aluminium chloride (pac) which is a a strong flocculant with a strong positive charge to agglomerate suspended particles.but the point is it is used as a a cougulant here not a flocculant.and there is a diffrance between these two

Let me explain the process below:



This note clarifies the application and dosing rates for the various different grades of polyaluminium chloride being sold in the UK.



Background

Filtration through a porous medium such as a sand bed is an efficient and cost effective means of reducing water turbidity. But sand filters are very limited in their ability to remove Cryptosporidium. Research at Swansea University for PWTAG in 2004 demonstrated the importance of coagulation in filtering out Cryptosporidium oocysts. Without coagulation removal rates in a single pass of a medium-rate filter were about 50%. This was dramatically improved, to over 90%, by dosing polyaluminium chloride.



Dosing rate

PAC is directly and continuously dosed from the containers in which it is delivered at a rate of about 0.1ml/m3 of the circulation flow. (It is very important that it is not diluted with water as it will form a gel.) This must be mixed as evenly as possible throughout the water flow.



Where to dose

Following dosing, coagulation of pollutants happens quite quickly. Flocculation is a slower process, where the coagulated particles come together in flocs, so it is important that there is sufficient time before the water reaches the filter media. At least 10sec is recommended, at a flow velocity not exceeding 1.5m/sec. This can normally be achieved in the space in the filter above the filter media. But to ensure the best possible mixing, PAC should be injected as far before the filters as possible – but after the place where the sample for the chemical controller is taken.



How to dose

For a pool with a capacity of 450m3 (100,000 gallons) and a turnover period of 2 hours the circulation rate is 225m3 per hour. The PAC dosing rate for this pool would be 22.5ml per hour. This is a very small quantity (two and a quarter 10ml test tubes per hour) and is difficult to dose accurately.



As you can see the tiny particles which are capable of escaping sand filter are turned into larger ones and being trapped in the sand filter



I hope TFP wont block me for this

 

[setsailsoon]

Amin,

Thanks, my experience is with floculant so different system. But I am skeptical that coagulant plus filter is a safe way to prevent cryptosporidium. Reduce yes, safe to swim no. But I'm sure you've considered that and as you pointed out this is definitely outside of what TFP is created for.

Good luck to you sir.

Chris

 

[Bama Rambler]

Thanks
Bama Rambler

Any specific brand you recommend?
Could you give me a link?

Without knowing what the normal operating pressure of your system at the location you're planning on installing the switch I can't make a recommendation. Also, the devices we have access to over here may not be available over there.