LP vs. MP UV Light

I’d like to take this opportunity to address one of the many issues surrounding the pool industry and UV lights.  First, all UV in not created equal and all water is not the same.  Water quality is the topic.  I have mentioned how I take creative ideas and apply them to UV and its uses.  I recall being laughed at for the merit to reflecting UV.  I remember in the early days being told, “Why would anyone make UV out of stainless steel?”  Of course, those folks now all have stainless systems and to hear them now you’d think they invented it.  lol

One of the topics I’d like to talk about today is Low Pressure UV vs. Medium Pressure UV.  You would think that after all these years that the truth would have settled this issue.  Truth being, that time has a way of bringing the truth to the surface.  In the question of LP vs MP in swimming pool applications the truth is finally has come to the surface.

In the beginning the world of MP systems with their many wave lengths and high power which was designed for very high flows in the millions of gallons per day and single pass situations like drawing water from large reservoirs for cities or raw sewage with all kinds of organic matter.

The thought that this same kind of application would be applicable to lower flows in pools and some other applications has proven to be wrong.  Wrong as in, MP is higher in replacement cost and a killer of All free chlorine and chloramines. MP has its world and LP has its world.  I understand the need and the want to grow your business, but being realistic is better in the long run.
I also understand that many have been talked into using the MP in this wrong application and they are finally realizing the huge cost associated with using this equipment.  Unfortunately, the desire to sell products far out-weighs the truth.  My mom used to say, “Son, some folks will tell you something 3 or 4 different ways before telling you a lie”!

Now, I’m not meaning to put down MP, but only correct the 3 or 4 different ways you may have heard about using it for the swimming pool world.   There are many applications for MP systems and they do a very good job.  My point is, that in flows below 1000 gpm and the leaving of free chlorine for reuse is not their world.  I foresee that LP will be moving into the higher GPM world very soon.  However, not to the level MP now handles.  Please review the below comparison below.

Comparison of Low and Medium Pressure UV

DESTRUCTION OF PATHOGENS (Bacteria, Viruses, Protozoan Cysts):
Both Conventional (low pressure) and Medium pressure UV will assist chlorine in disinfection including the destruction of bacteria, viruses and protozoan cysts on a single pass. Cryptosporidium only requires 12 mJ/cm2 to inactive.  Sentry lamps at EOL (end of lamp life) produces more than double this amount.

Monochloramine (NH2Cl), Dichloramine (NHCl2), and Nitrogen Trichloride (NCl3) are the products of nitrogen introduction from bather waste forming ammonia (NH3) and reacting with chlorine.  These, when combined with chlorine, are the complex contaminants responsible for eye burn, disagreeable odor, poor oxidation, and a host of other problems in the swimming pool water, building and equipment which houses the pool.  This is a “progressive” compound, which means mono-chloramine forms before it can form di-chloramine or tri-chloramine.

Low Pressure UV destroys all organics including mono-chloramine.  The destruction of mono-chloramine prevents the formation of additional forms of chloramines. LP also produces at 185nm that creates other oxidative molecules that offer better control of chloramines.  MP does not offer UV below 200nm.

Medium Pressure destroys all organics and all compounds of “chloramines” this also includes free chlorine on a single pass.

Low Pressure UV does not destroy the active free chlorine that is needed for oxidation and disinfection on a single pass.
Medium Pressure UV will destroy a minimum 30% or more of all free chlorine as it passes through the chamber, thus multiple passes and free chlorine is gone.  Which means you are constantly having to add more chlorine to maintain any level needed to meet requirements.

Not all low pressure lamps are “Amalgam” lamps. Amalgam lamps provide a higher intensity of UV light over conventional UV, providing additional power to destroy organics in warmer water up to 130 degrees F.  The Sentry lamps are 25% 185nm and 75% 254nm. 0-3 from 185nm offers additional oxidation for better water quality.

Medium-pressure UV lamps require over 3 times the electrical power than low-pressure lamps.

Low-pressure lamps last three (3) times longer than medium-pressure lamps.
Low Pressure | Medium Pressure
(Cosmic Rays, Gamma Rays, X- Rays) (Ultraviolet Rays)Visible (Infra-Red) Radio Waves)

Ozone production @ 185nm and at 245nm NH2Cl mono chloramines destruction…295nm HOCL free chlorine destruction….
Our Sentry UV’s stop at the 260nm range while MP continues to put out some of all the UV range starting at around 200nm, thus wiping out free chlorine.  This is an additional cost of operating your pool. Of course this is not a bad thing if you are also selling chlorine.  That’s the best of both worlds, but not right!

Understanding this bit of knowledge will better help you plan your UV purchases.  So, once again, I’m not knocking MP UV systems.  My objective here is to educate you, the user of UV, to your best advantage in every way possible.  I hope this has helped and feel free to contact me if I can be of any further help.

Yours for better UVing,

Roy Underwood

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