Calibrating Pump/Venturi (Air) in a Closed Recirculating Water System

[AyVent]

TL;DR Summary

I am building an experimental closed RAS. However, despite my best efforts, I faced issues with the pump/venturi calibration. The system will need plumbing changes but I need advice to plan the best course of action. Help is greatly appreciated.

Hello,

I am building an experimental closed RAS. However, despite my best efforts, I faced issues with the pump/venturi calibration. The system will need plumbing changes but I need advice to plan the best course of action. Help is greatly appreciated.

Here is an overview of the system:

The cycle goes like this: sump tank> pump> venturi (air)> oxygen saturator> tank> sump tank

Sump tank: a standard 1m3 cylindrical PE tank buried about 90 cm underground with about 30 cm aboveground. Inlet to the pump is an inverted L shaped 1 inch PE pipe with check valve installed.

Pump: 1/3 hp pool pump with a low head high flow curve. Currently one is installed but plan was two in parallel. It also has an automatic pump control (APC) to protect from dry-run and heating issues. (Both attached)

Venturi: Mazzei 1584-A PP (attached)

Oxygen Saturator: design followed as is from a SARE project results ( https://projects.sare.org/project-reports/fnc20-1207/ ) (also attached)

Tank: h: 0.65 m L: 27m W: 2.4m; an open inlet pouring down 1.3m above tank level with an overflow 4 inch outlet at around 0.58m height. (some system pictures are attached)



My issue is that the APC keeps cutting off the pump a few secs after operation. I tested the pump using a hose and it worked normally. There were leaks close to the venturi and they were fixed. But I suspect they might be leaking air still. I then reviewed the Head calculation of both the system and the pump.

System Head was around 4m and the pump curve starts at 4m Head at max flow. So, I tried to adjust the valves until the Head was workable or comfortable for the pump. And it worked with all valves mostly closed but I shut it down after 20-30 mins. After a couple tries of this, it just wasn’t consistent to get it to work this way. And the venturi was blowing bubble at this state. No suction at all. Tbh, I originally designed the piping for future expansion and the resulting increase in flows but this caused issues.

Aside from obviously increasing the system head, what steps do you think should be done to test for and modify to ensure normal operation?

Excuse the rough work, I am from a business background but with a certificate in RAS from Cornell.

And again, thanks for all the help.

 

[jrmichler]

TL;DR Summary: I am building an experimental closed RAS. However, despite my best efforts, I faced issues with the pump/venturi calibration. The system will need plumbing changes but I need advice to plan the best course of action. Help is greatly appreciated.

My issue is that the APC keeps cutting off the pump a few secs after operation.

1) What is RAS?
2) How does the APC work? Does it sense pressure, water level, flow, or what?
3) The APC photo shows two different cables and what appears to be some sort of connector. What are the inputs and outputs to each of those?
4) Where is the APC connected in the piping diagram titled "Venturi and saturator design.pdf"?

System Head was around 4m and the pump curve starts at 4m Head at max flow. So, I tried to adjust the valves until the Head was workable or comfortable for the pump.

5) Is your pump the curve labelled 0.33 CV? If so, there is nothing wrong with running at 4 m TDH. But, just to be sure, show on the piping diagram where the pump head is being measured and also indicate the water level relative to the pump. Which valve or valves are you adjusting?

Aside from obviously increasing the system head, what steps do you think should be done to test for and modify to ensure normal operation?

6) Add pressure gauges before and after the venturi. There is something strange with the venturi performance table. For a single inlet pressure, it shows the same flow rate for a wide range of outlet pressures. This does not make sense because the flow rate should be a function of the water pressure drop from venturi inlet to outlet. Also, the the air suction flow flow should be a function of the air inlet absolute pressure. I suggest that you talk to a sales engineer and clarify the injector performance table for your injector.