sump pump back up system

With the Liberty you have a back up pump and power outage protection? It may flip back and forth to put equal run time on the pumps??

Sounds like the Pump Sentry is just a power outage system. So if the one pump fails and power is out??

How much protection do you want? $$

Are you a lucky person?

Start off by defining the failure mode you are trying to protect against. The two systems mentioned protect against entirely different failure modes, so they are not comparable in any way.

A pump failure? OK, then dual ALTERNATING pumps, with an alarm set at the level where the backup pump turns on, is the way to go. (most alarms are set way too high, by the way). The Liberty unit you note is NOT such a system.

A power failure? That sort of assumes the power is out but the pump is working. The Pump Sentry seems to do that, and so does the Liberty — the difference being the Liberty has a second pump running off the battery. Either would be a good choice solely for a power failure.

The water eductor — basically a jet pump — which @mattmia2 mentioned is an excellent choice for a power failure scenario — if your water supply stays on.

But — as I say, first define what failure mode or modes you are trying to protect against.

A comment relative to "Backup" pumps" and maintenance. my humble opinion, there really is no such critter. I've designed a few dozen systems — granted, larger — over the years and also run systems.

Dual pumps, yes. Quite common. But they are DUAL pumps. Either pump is capable of doing the required job. They are arranged with automatic level controls, and the lead pump alternates with EVERY cycle. The levels are set as follows, from dry or near empty going up.. 1. Lead pump off. 2. Lead pump on. 3. Lag pump off. 4. ALARM. 5. Lag pump on.

Any other arrangement and two things WILL happen, both bad. First, One of the pumps will fail to operate. Two, you won't know about it until both pumps fail.

I've seen that failure mode in systems ranging from humble little sump pumps in someone's basement to small sewage ejector pumps where the septic system is uphill from the house to million gallons per day water supply and wastewater systems.

The two keys to success are simple: the pumps alternate lead and lag on every cycle — and the ALARM goes nuts BEFORE the lag pump is called on.

we have the same issue with multi lamp projectors. no one notices that the other lamps have failed until the last lamp fails.

Sadly true. So where you have just that one cramped sump pump pit (which also may mean that the pump endures a lot of cycling), as you say you just have to live with it. High water alarm in the basement or whatever, and keep everything which might get damaged well raised off the floor…

Wouldn't just running a generator to run your normal pumps make more sense than a lpg powered air compressor?

i have enough trouble finding someone that can fill a propane tank that is open when I need it when there isn't a power outage. propane seems like a terrible fuel source. I figure given my rate of gasoline consumption that I would use about 25 # of propane a day. It is a lot easier to find a gas station than a propane distributor after a disaster.

unless there is a huge efficiency drop off in propane, a 100# tank would probably take me through the longest outage that we have had which was 4 days. I go through around 5 gallons of gas in a day. A pound of propane is equal to about .18 gallons of gas so that is 111# of propane. I have a 5kw generator but it is running at more like 500w most of the time, the 5kw is mostly for motor starting. It is stupid easy to add propane or natural gas to a gasoline generator. Adding a tap to connect it to the natural gas line to my grill is probably the more practical solution. Then there is the complication that a generator in most applications is only going to draw its full rated volume of gas for a few seconds or less when a motor starts.

How do I obtain gasoline when there's no electricity?

Won't you use an engine driven air compressor more often than a backup pump?

Your Dairy Queen sells gas?!?

turning a gasoline engine in to a tri fuel engine just involves putting an orifice block between the carb and air cleaner and adding a gas regulator. you can buy a kit for a couple hundred bucks.