Sand Filter Glass Bulb/Sight Glass

by Doug

Sand Filter Glass Bulb/Sight Glass

by Doug Maluchnik
(Blairstown, NJ)

Question about sight glass on a swimming pool sand filter. I wanted to use the waste control on the filter as I was vacuuming my pool for the first time this season to remove the dirt on the bottom. I noticed that the glass bulb on the sand filter is leaking and never noticed this before. Looking at the bulb it is fine and where it screws in seems to be fine.

I also noticed that when the filter is in normal operation that the same glass bulb does not have water running through it like usual. Has my valve gone bad?

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Thanks for the question Doug. First, when you're vacuuming to waste keep an eye on the water level. You're creating a virtual siphon of pool water when you vacuum to waste so keep the water level between 1/3 - 1/2 up from the bottom of the skimmer.

This will cause the pump motor to not have enough water and will reduce your water flow (gallons per minute or GPM). Be sure to snug up, but not over-tighten the screws on the sight glass. If it's still leaking you can take it off and it may have an O-ring or gasket that is easily replaced.

Check the skimmers baskets for debris and be sure the pump basket is cleaned and positioned properly. Also check the pump basket to make sure it's not cracked as this will allow debris into the pump's impeller.

To check the impeller, turn off the power to the pump motor and the breaker. Reach in and remove the basket and into the opening to feel if the impeller is clogged with debris. If you can't feel it you may need to remove the motor from the pump and inspect the impeller. It should turn freely.

You can also install a water flow meter to measure the GPM to be sure you're getting the correct amount of water flow. Normally a good rule of thumb for understanding your GPM is this:

Pool size divided by 10 divided by 60 equals flow rate. So, a 25,000 gallon pool divided by 10 hours of filtration will equal 2,500. Take 2,500 and divide that by 60 minutes per hour and you'll get 42 gallons per minute.

Also be sure your filter is clean and backwashed properly. If you have a cartridge filter be sure to clean them or replace them with new filters.

This will give you a good start and if you're still having issues you may want to get professional pool tech to have a look. But at least you'll know what to look for.