Gravity backwashing

[Rollercoastr]

I've been operating with the assumption that my plumbing setup is unique, and therefore my backwashing process is different than most. I want to run this by the experts to make sure.

My pool equipment is in my basement, below the level of the pool. When I move the valve to backwash, the flow to waste through the 2" drain hose is strong without the pump. I've only turned the pump on once during a backwash, and it increased the flow so much that the waste hose "levitated" and shot out of the floor drain. Since then, I've let gravity do the work during backwash and rinses.

Not having a basis of comparison of how much flow to expect, I'm not sure if my 2.5 - 3 minute, gravity-driven backwash cycle through a 2" hose is appropriate.

I'm wondering if I should secure the waste hose and run the pump, or extend the cycle time and continue to use gravity.

 

[atttech-2]

I don't have a DE so can't answer the flow question but if a DE owner comes along and says you need a bit more flow you could think about putting a spigot between the output of the pump and the multi port that would allow you to connect a garden hose using a female to female hose and control the pressure from your home water supply.

 

[Rollercoastr]

It's a sand filter.

 

[atttech-2]

Should have read the signature

 

[JamesW]

How far is the pump below the pool surface?
What is the total HP off the pump?
What is the surface area of the filter?
What is the filter pressure with the pump off?
What is the filter pressure with the pump on?

 

[Pool Clown]

Good backwashing needs good flow to dislodge your dirt and debris. If you can accomplish this with gravity and a momentary push from the pump, who am i to say it is not enough? What you do want to do is observe the waste water. If it is clear all the time, your not getting enough velocity to move the dirt. Now you have an indoor pool. You may not be getting the dirt or the amount "murk" that outdoor pools receive. Especially if you are backwashing often. But i think you should be getting a little bit of off color water when the back wash water first begins to exit the pipe, then slowly clear up. At this point, i usually stop flow (this may be a bit of a challenge for you), for a few seconds, then start the pump again and observe the output. Repeat that process until you get clear water upon restarting the pump.

I guess the bottom line is this, if what you are doing now results in clear water and not overly excessive pressure on the filter, i would suspect that how you are managing the filter is ok.

Note: Keep in mind that your equipment is below the water line, and that you will run a certain amount of static pressure ALL the time.

For the benefit of others, i would not take away from this, that this is the proper procedure since indoor pools and equipment below level is the exception, not the rule, with regard to the majority of pools out there.

I often get questions from long time pool owners as to if they are doing things right. All i can do is look at their crystal clear pool with my arms out stretched at the pool, and say... "You tell me".

 

[Rollercoastr]

How far is the pump below the pool surface?
What is the total HP off the pump?
What is the surface area of the filter?
What is the filter pressure with the pump off?
What is the filter pressure with the pump on?

The pump is apx 9' below the surface of the pool.

I don't know the HP of the pump. I need to clean the label and take a better look.

The surface area of the filter is 3.14 sq ft

The resting pressure reads 6 psi

The running pressure was 27 psi when I took possession of the house almost 3 weeks ago. It went to 31 after I began the SLAM. I've performed 3 backwashes since, and the pressure has come down to 24 psi.

 

[Rollercoastr]

I guess the bottom line is this, if what you are doing now results in clear water and not overly excessive pressure on the filter, i would suspect that how you are managing the filter is ok.

That makes a lot of sense.

I have some "complications" that make a judgment call challenging right now. The pool was highly neglected, so I assume the filter was as well. I don't know the normal pressure for this setup. The water is not clear and the slam is taking a long time, but I haven't been an outstanding TFP'er. I've left it on wkds, I had a slow start brushing and vacuuming and the pool has Br content.

 

[Rollercoastr]

I've been gravity backwashing for about 3 minutes. The water starts clear and then looks like dirty dishwater, and then runs clear again. Pressure only decreases 2-3 psi after I rinse and restart the pump.

 

[JamesW]

Your ideal backwashing flow rate is about 45 gpm. Gravity backwashing is probably not enough and with the pump on is probably too much. With too much flow, the main risk is losing sand. I would suggest removing the filter top and checking that the sand level is good.

 

[Rollercoastr]

Gravity backwashing is probably not enough and with the pump on is probably too much. With too much flow, the main risk is losing sand.

That's what I was afraid of. Is there a preferred method of measuring flow rate? I'm thinking one way would be to multiply the time required to fill a 5 gal bucket. Another would be measuring level loss in the pool level during a drain
related to surface area...?

 

[JamesW]

Try the bucket test if practical. You will probably get more than 1 gallon per second.

 

[Pool Clown]

You wouldn't want to regulate the flow while backwashing. Your flow rate would be determined by your pump hp (hopefully at time of design). I would't worry if you lost a little sand each time. You shouldn't need to backwash so frequently once you get things under control. Try backwashing the filter with the pump and see if you get better results, like more "dish water" or rather longer dishwater duration before it clears.