How It Works: Pool Vacs

Hayward ® Pool Vac UltraA “pool vac” is a self-propelled underwater device for cleaning the bottom of swimming pools. The device itself is complicated in its number of parts, but simple in operation. Figuring out how it really works – its care and feeding – has taken me many years. Most of us don’t own pools. We would not be expected to have much curiosity about the hot-climate suburban lore of pool maintenance.

In Phoenix we’ve been through three Hayward® brand pool vacs. I’ve struggled throughout the years to understand why sometimes “Hayward”, as we always anthropomorphised the little device, worked superbly – and sometimes didn’t work, or hardly worked, at all.

Hayward is just one part of a delicate system. If the pool isn’t healthy, Hayward is going to get sick. In a rare “eureka moment” I saw the answer to my question: trying to “fix” Hayward is only going to buy a few hours or days of smooth operation. A happy Hayward is the result of many things working well together: pool pump pressure, the condition of the skimmer and filters, the amount of unfiltered debris at the bottom of the pool, the pH and condition of the water, the age and condition of 40 feet of umbilical hose, and wear and tear on Hayward’s moving parts.

Holy cow, that’s what the doctors have been trying to tell me for years about my own body.

Hayward ® exploded view

Hayward is powered by the water flow in the suction hose, which is fitted on the other end to the pool skimmer. The water flow also carries away dirt and debris collected by the vacuum on the underside of the unit, as Hayward scoots along the pool bottom. An internal geared water wheel, a simple water turbine, drives the moving parts – visibly, its flapper “wings” and footlike “shoes”.

These parts help Hayward to glide just above the pool bottom. The flappers help prevent Hayward’s vacuum suction bottom from clamping onto the bottom by creating a thin boundary layer cushion of water. The little natural rubber feet help Hayward to push off from the bottom, and may assist in forward motion. Channels in the flat bottom plate seem to intake water more from the front of the unit than the rear. The net effect, however engineered, is a modest forward motion of about 6-8 inches per second.

The Hayward unit vacuums along the bottom in a random path, and will actually clean more than 70% of our pool in the first hour of operation. It is also programmed to spend about 20% of its cleaning time on the walls of the pool. Hayward’s bumpers are also programmed with a modest obstacle avoidance system: if it gets “stuck” pushing against pool steps, for example, it will eventually muddle itself around and scoot off in a different direction.

What Can Go Wrong?

Pool algae is a killer. If your water “gets away from you” and you get an algae bloom (excessively hard water; pump stopped or clogged), this also coats Hayward’s moving parts. It will stop, slow down, or get “stuck”.

Chemicals: Chlorine in moderation keeps pool water clean and algae-free, such as is supplied by the chlorinated “tablets” everybody has seen at hardware stores everywhere. When you “shock” a pool, you are trying to regain control of a water problem, which may involve adding massive doses of liquid chlorine or dry “shock” powder. This is rough on plastic parts. Hayward should be taken out of the pool before a shock treatment, but often isn’t.

Pump pressure is everything. Too little pressure, and there is not enough suction to operate or propel Hayward. Our pump’s rating will never deliver too much pressure, but that could cause excessively rapid operation or perhaps its suction would just cause Hayward to clamp to the bottom. When Hayward inexpicably slows down or stops, and cleaning its intakes doesn’t correct the problem, that usually means it’s time to check the pump basket filters, or perhaps even backwash the sand filter.

Wear and tear: Below-ground (excavated) pools are generally lined with gunite, a sprayable form of a sandy concrete mix. Some pools are resurfaced with a pebble texture. This causes wear of Hayward’s flappers and feet as it scoots along the bottom. The flappers have stamped wear indicator marks to indicate when they have been abraded down to replacement level. It appears that, in this pool, flapper replacement every year would be a good idea. I was surprised how much effect this has on the spriteliness of Hayward’s forward motion underwater. The flappers look much the same worn as new, which supposedly explains how our 3-year old “backup” Hayward’s flappers had even the indicator marks completely ground off.

Everything’s Working

This spring, everything’s working in synch, like a good little ecosystem. I had the pool drained and refilled last winter, eliminating a hard water problem that caused uncontrollable algae bloom. The pump fittings are in good repair. I backwash periodically. The filters are cleaned regularly. Pool water level is right where it should be. And Hayward is back from a repair and tune-up (free – under warranty) with new shoes and flappers. He scoots merrily along, gobbling up wind-blown stuff as fast as it can get into the pool. Every part of the system is working well to contribute to the success of each other piece.

And that’s what was so hard for me to grasp. Oh, sure, if the filter baskets are a little full, or the pool water’s a little low, or I haven’t backwashed in months, Hayward still operates, pretty much, though not well. If all of those things are in dire need of attention, Hayward may work slowly, sporadically, or not at all.

But, it’s a system. Grasping that every part of the system is important is easy. Grasping how interconnected and interdependent everything is – that took a little longer. As with human medicine, we can’t just say “we’re going to ignore your blood presure and just reduce the pain in your knee.” To steal the old doctor’s gag, if I’d known I was going to live this long, I would have taken better care of myself.

Hayward ® happily at work in our pool

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