Wastewater pumps, you know you need them. But which type of pump should you use?
There are two basic pumps types for this discussion. Centrifugal or submersible. They obviously work great, but life is never perfect. (This page is a work in progress, stay tuned. Dec 5, 2019)
In the world of wastewater, plugging is always a concern. All pumps are subject to plugging from solids such as pallet chunks, shrink wrap, keg caps, etc. Even a mass amount of spent grain can plug a pump. The easiest and cheapest way to control this problem is screens in your floor drains and even a basket under the outlet pipe in your lift station. Read more below.
(A grain of salt here. Remember we are talking about brewery wastewater, and usually small breweries. Large scale wastewater pumps are not included below.)
As you can probably guess, these pumps sit on the bottom of the wastewater tank.
There are several types of submersible wastewater pumps.
- Effluent – Generally designed for smaller solids
- Sewage – Generally designed for larger solids
- Grinder – Engineers frequently look at grinder pumps for a brewery lift station. This is usually overkill, if you can keep large solids out of the lift station (pallet chunks, shrink wrap, keg caps, etc.) there is no need for a grinder.
With any standard submersible pump, they should last 2-3 years. Not very long, but they have a tough life.
Cast iron pumps have the shortest life. Cast iron is subject to corrosion, often the side of the pump volute will wear through to the point of failure.
Stainless steel and plastic pumps handle the corrosive effects much better. After several years of operation they will still look brand new. As odd as it sounds, the weak link is the cord; the sheath bubbles and leaks, leading to a short circuit. Pumps with a custom cord are available, but long lead times and added expense is usually not worth it.
All submersible pumps have an upper temperature rating. Since the pumps are submerged the water is the cooling media for the motor. Brewery wastewater is generally hot to very hot, see here. The submersible pump should be rated for these temperatures.
An almost required device for a submersible pump is a slide rail system:
The foot mounts to the bottom of the tank, and a hook adapter mounts to the pump. The hook slides on the rails and adapts to a pipe fitting on the foot. The pump sits close to the bottom, but not on the bottom of the tank; the weight of the pump and motor maintains the seal between the hook and the foot. This system allows for easy removal and replacement of the pump, no tank or confined space entry needed. These systems are inexpensive and super handy.
Benefits of a submersible pump:
- Installation is easier. Less piping.
- Can be submerged.
- Priming is not a challenge.
Drawbacks of a submersible pump:
- The motor, cord, and pump is subject to the water itself which is generally hot and corrosive. Ultimately this leads to a shorter pump life.
- Out of mind, out of site isn’t always a good thing.
- Subject to large solids, high temperatures,
- Access can be difficult.
- Is it running? Not very easy to tell.
- Generally requires a slide rail mounting system.
- Generally not serviceable, consider them disposable.
- Generally only electric powered.
- Installation is trickier. Piping needs to be aligned correctly.
Submersible pumps have their place in life. But it’s a hard life for them and sucking up a chunk of pallet wood is a frustration most of you have experienced.
This is what most of us think of as a pump. It mounts to the floor horizontally with piped connections in and out of the pump. There are about 1001 types of centrifugal pumps, but remember we are focusing on brewery wastewater here.
The first design criteria is the pump should be designed for wastewater. This usually means an open face impeller. You lose some efficiency, but almost no chance to plug the vanes. The impeller should be made of stainless steel and I recommend a stainless steel pump head. Long life is what we’re after.
The motor should be TEFC (totally enclosed, fan cooled), which means you can hose it down. Again you lose some efficiency this way, but an open motor is asking for trouble.
Benefits of a centrifugal pump:
- Only the pump head is subject to wastewater contact.
- Proof of operation. You can hear the pump running.
- Access. It right there, sitting on the floor. You can see and feel it.
- Serviceable and long life. The seal is replaceable (with some skill), the pump should last many years.
- Electric or portable and gas engine driven.
- Temperature isn’t a problem for the pump, but can be a problem for the piping.
Drawbacks of a centrifugal pump:
- Priming. Priming isn’t a problem for a pump with flooded suction. However if the pump is installed above the tank, priming can be an issue. Self priming pumps are available.
- Noise. Pumps usually aren’t super loud, but between the motor, fan, impeller, and moving water then can be noisy.
- Space. This pump gets mounted to the floor and real estate is always an issue. It’s also subject to damage from forklifts, pallets, falling kegs, etc.
- Leaks. The pump will leak sooner or later. At the threaded fittings and/or after the pump seal starts to fail.
- Pump head may be subject to freezing.
A third type of pump is a line shaft pump. This would be for a lift station, and it’s the best of both worlds. The pump head is submerged at the bottom of the tank and the motor is above grade away from the hot and corrosive water. Lots of benefits to a pump like this, the biggest drawback is cost, $10k-$20k per pump(!). See the sketch at the bottom of the page for what they look like.