Corrugated hose or smooth for bilge pumps?

[Mithril Bham]

Originally Posted by bobmcd625

Any recommendations as to which type or brand of smooth bore tubing one should use?
I recently replaced a bilge pump discharge tube using the cheapest corrugated tube at West Marine but am having second thoughts. I intend to add a second pump as backup so I could at least have one with the best line.

The most expensive.

[Lepke]

I'm finishing changing all my bilge hose with schedule 80 plastic pipe from corrugated hose. Where I need an elbow, I use a sweeping fitting or heat the pipe and make my own. Pumps now produce a visually higher amount of water.
The reason for not using a check valve in a bilge system is that small debris will get caught in the seal and allow water to drain back into the bilge if there is no loop with a vacuum break and the thru hull goes under water. If an unmanned boat is sitting with a small leak or rain and the battery goes dead (power failure, etc), once the thru hull goes under water (with no loop and vacuum break) the boat fills. Many boats have been sunk for this reason.

[Cheechako]

Originally Posted by Exile

OK, that makes sense. I have a couple of those installed vertically in gravity-fed sink drains and I periodically need to tap on them with a hammer to free them up. Then they work again for awhile. They're only there to keep saltwater from splashing up into the sinks under heel, so not exactly mission critical. When they do stick, they stick in the closed position (like in your case) so freshwater from the sink cannot drain. Probably not advisable in a bilge pump application, even if installed vertically.

Bilge pumps are notoriously poor at pushing against resistance. Essentially they are a centrifugal pump, but with a fairly open housing around the impellor. The flapper in the bronze valve is quite heavy actually, so I installed it horizontally. It was very free to swing with no resistance. The problem was the system siphoned water into the hull when the boat was heeled! No debris in the valve when I removed it. I guess being horizontal, it allowed water to flow past the flapper as there was not much "head" keeping it closed! So either you get resistance to flow mounted vertical or run the risk horizontal. I went back to a loop.

[mitiempo]

If at all possible the bilge pump outlets should always be above the waterline - at any angle of heel. This leads to the transom if you can achieve this.

[Exile]

Originally Posted by Cheechako

Bilge pumps are notoriously poor at pushing against resistance. Essentially they are a centrifugal pump, but with a fairly open housing around the impellor. The flapper in the bronze valve is quite heavy actually, so I installed it horizontally. It was very free to swing with no resistance. The problem was the system siphoned water into the hull when the boat was heeled! No debris in the valve when I removed it. I guess being horizontal, it allowed water to flow past the flapper as there was not much "head" keeping it closed! So either you get resistance to flow mounted vertical or run the risk horizontal. I went back to a loop.

OK, I get it. I've always had the loop with a siphon break (at the transom high point), but it doesn't seem to hold the water in the line from falling back into the bilge. I figured it was more for preventing seawater from entering from behind the boat. Every boat is different, obviously. I'd prefer to dispense with my check valve for reasons well stated, but I think it means going to a different type of pump.

[Terra Nova]

Originally Posted by Exile

...I've always had the loop with a siphon break (at the transom high point), but it doesn't seem to hold the water in the line from falling back into the bilge...

The discharge line should rise from the pump directly to its highest point and then slope to the outlet. You can add a small diaphragm pump to dry the bilge.

[Exile]

Originally Posted by Terra Nova

The discharge line should rise from the pump directly to its highest point and then slope to the outlet. You can add a small diaphragm pump to dry the bilge.

I described my set-up in post #21 & in several posts thereafter. It is as you describe. Drying the bilge from the water that falls back from the line runs the risk of my Rule 2000 centrifugal pump cavitating.

[Terra Nova]

Originally Posted by Exile

...Drying the bilge from the water that falls back from the line runs the risk of my Rule 2000 centrifugal pump cavitating.

No, it doesn't, unless you have a check valve, which you shouldn't.

[Exile]

Originally Posted by Terra Nova

No, it doesn't, unless you have a check valve, which you shouldn't.

If no check valve then all the water in 16' of 1 1/8" diam line falls back into the bilge & cycles the pump continuously. It's a deep, narrow bilge with a steep climb out, and then a lengthy, continuously rising run to the above-waterline siphon loop at the transom. It amounts to approx. one gallon of water. Any suggestions on how to deal with this?

[Terra Nova]

Originally Posted by Exile

...Any suggestions on how to deal with this?

I've already told you--make the highest point in the line occur above the pump--not at the transom.

[Exile]

Originally Posted by Terra Nova

I've already told you--make the highest point in the line occur above the pump--not at the transom.

The transom IS the highest point above the pump. I don't think you're understanding my setup, or maybe I didn't describe it well enough. But thanks anyway.

[Terra Nova]

Originally Posted by Exile

The transom IS the highest point above the pump...

That is precisely your problem. The discharge line should run DOWN to the transom from a high point above the pump.

[Exile]

Originally Posted by Terra Nova

That is precisely your problem. The discharge line should run DOWN to the transom from a high point above the pump.

If the transom IS the highest point then it's axiomatic that there's no higher point for the line to run down to.

[Terra Nova]

E--you seem to simply want to argue, rather than accept help with your poorly installed system. Obviously your transom mounted bilge pump discharge is not the highest part of the boat.

Unsubscribed.

[Exile]

Originally Posted by Terra Nova

E--you seem to simply want to argue, rather than accept help with your poorly installed system. Obviously your transom mounted bilge pump discharge is not the highest part of the boat.

Unsubscribed.

Hmmm . . . maybe T-N wanted me to run bilge hose up to the bow first before running it back down to the transom? The bow is slightly higher. Maybe up one of the masts? That's definitely higher! Or maybe I just misunderstood. More interested in figuring this stuff out than arguing . . . really. It's a critical boat system.