A Quick Word on Dip Tubes

by Richard Garcia, Director of Research, Reaction Research Society

I’ve had the opportunity to talk a lot with many amateur rocketeers getting into building liquid rockets. Because many commercial pressure vessels only come with one port, you often have to choose between making or modifying a pressure vessel. I always see a third option, dip tubes, being over looked.

I would not recommend using a dip tube on a flight vehicle, but they are quick to put together for a test stand. A dip tube can be made from two parts: a tee fitting and a modified compression fitting.

Compression fittings do not normally have enough room to send a tube all the way through them. Most compression fittings purposefully have a stop to bottom out the tubing at a specific depth within the fitting. Usually these compression fittings have enough meat on them to drill through and open their internal diameter to fit the tube straight through them.

Cross-section of a compression tube fitting, before and after drilling
Typical compression fitting before and after modification to allow the tubing to fully penetrate the fitting. The stop feature is common which makes tubing joints repeatable and accurate. This internal diameter is opened up drilling to allow the tube to pass completely through. Note that the compression fittings shown have a tapered pipe connection (NPT, typically). Other pipe or tubing connections are possible depending on the fitting manufacturer.

Putting this modified compression fitting along the straight path of the tee fitting will allow you to pass a tube through both fittings and into the tank itself. The tee connects on to the tank’s port and the tube goes down to just above the bottom of the tank (if connecting at the tank’s top). The branch of the tee feeds the tank ullage space with pressurant gas and the tube picks up fluid from the bottom of the tank as long as the liquid line is above the tube opening.

Dip tubes on top and bottom of tanks
Dip tubes shown in both top and bottom mounted configurations. Note that the fluid passes from the annular opening on the tank bottom mounting configuration. Note that the pressurant gas flows through the annular gap in the tank top mounting configuration. The tee fitting shown has tapered pipe fittings (NPT, typically).
Illustration of a dip tube mounted on top of a liquid filled tank
Illustration of a top mounted dip tube on a liquid filled tank. Pressurant gas is supplied at the branch connection of the tee fitting and flows into the ullage space through the annular flow path. The liquid is driven up the central tube and out of the tank if the gas pressure is sufficient to overcome the liquid head and tube friction.

This can be flipped upside down, pressurizing through the tube and flowing the liquids out of the tee branch connection. It is always important to consider the amount of flow area in the tubing you are using as well as the annular flow area created by this combination of fitting as it is likely to be the area of minimum restriction to flow.

illustration of dip tube used in pressurized expulsion of liquid from a tank
Illustration of a dip tube mounted on the bottom of a liquid filled tank. Pressurant gas flows up to the top into the ullage space of the tank expelling the liquid from the annular flow path in the tee fitting and out of the branch connection.

Also, instead of a tubing connection, one could put a thermocouple through the compression fitting of the proper size to make an internal fluid temperature measurement in the tank either immersed in the liquid below or measuring the ullage gas temperature in the top of the tank. This is a convenient way of mounting a temperature sensor.

P.S. Here are two kinds of tanks with ports on each end that are readily available. Try looking for automobile air tanks like this one from Speedway Motors:

https://www.speedwaymotors.com/Speedway-24-Inch-Aluminum-Air-Suspension-Tank-4-Gallon,126697.html

Or a gas sample cylinder such as this one from Swagelok

https://www.swagelok.com/en/catalog/Product/Detail?part=304L-HDF4-1000

For questions, contact Richard at

research@rrs.org

RRS visit to Additive Rocket Corporation

The Reaction Research Society (RRS) was glad to receive an invitation to an open house held by the Additive Rocket Corporation (ARC) in San Diego on November 13, 2018, which invited guests from academia and industry to have an exclusive look at the company’s business. The event was co-sponsored by the University of California San Diego (UCSD’s) Atkinson Hall Prototyping Laboratory. It was well worth the long drive through south-bound traffic from Los Angeles to arrive at UCSD by early evening.

Additive Rocket Corporation in San Diego, CA

Additive Rocket Corporation

The welcoming speech was given by Dr. Jeff Sundabrae showcasing the Atkinson Hall Prototyping Laboratory at UCSD and proud partnerships that they have cultivated.

Andy Kieatiwong, CEO of Additive Rocket Corporation, and Dave Nordling, Secretary, RRS

Andy Kieatiwong, CEO of ARC, gave the headline speech about his new company, founded in partnership with his friend and colleague, Kyle Adriany.

Kyle Adriany, CTO of Additive Rocket Corporation (ARC)

ARC uses a proprietary iterative design process that takes advantage of the freedom in design offered by additive manufacturing. ARC has developed their own software algorithms that can rapidly analyze and compare a wide range of design alternatives very quickly which ultimately leads to a few highly efficient designs that should enable a low cost, high performance rocket to be made.

ARC is a small start-up in San Diego. Several of their engineers and experts were in attendance at the event as ARC showed the audience their mission to produce high impulse, ultra-low cost additively manufactured engines. Many of the guests were fellow researchers at the Prototype Laboratory and UCSD. The most exciting part was getting a tour of the university laboratories and the shared space that ARC has with their EOS M290 large scale metallic 3D printer made by Electro Optical Systems (EOS). It is an amazing piece of technology to observe in action.

Electro Optical Systems (EOS), M290 industrial 3D metal printer

An uncooled thrust chamber prototype of a 125-lbf rocket motor, made by ARC’s 3D printing machine in Inconel 718

ARC has already built their first prototypes and is planning a series of hot fire testing of their “Nemesis” engine, hopefully at the RRS Mojave Test Area (MTA), in the very near future. With successful rounds of testing to anchor their design algorithms, ARC should be able to offer a powerful and elegant rocket at very competitive prices to a growing marketplace.

Additive Rocket Corporation’s “Nemesis” engine

I was glad to attend the event and greatly appreciate the hospitality of ARC and UCSD. Many found it very exciting to witness firsthand a remarkable material process that is slowly and surely changing the manufacturing marketplace.

The RRS is hopeful that ARC will attend and speak at our forthcoming 2019 RRS symposium in April. Stay tuned to our website for further updates from ARC and the 2019 RRS symposium at the Ken Nakaoka Community Center in Gardena.

RRS at the Two-Bit Circus in Hawthorne

The Reaction Research Society (RRS.ORG) was proud to participate at the Two-Bit Circus event held in Hawthorne, California on Saturday, May 19, 2018. The Two-Bit Circus Foundation is a STEAM (Science, Technology, Engineering, Art and Mathematics) Carinval designed to inspire young people into STEAM careers to learn practical skills and build the things of imagination.

Two Bit Circus – Hawthorne 19-MAY-2018

The RRS was proud to be at the Two-Bit Circus STEAM Carnival in Hawthorne (5/19/2018)

Osvaldo, Frank, Max and Russell were at our booth at the event introducing people to the RRS and our passion for amateur rocketry. We had one of our standard alpha and standard beta rockets on display.

The RRS also brought an upgraded air rocket launcher which was used to propel small paper rockets to great heights. It was wildly successful with over the 100 kids that stopped by the RRS exhibit.

Frank’s T-shaped air launcher

The RRS was proud to hoist our banner at the event. We are thankful to the Two-Bit Circus Foundation for their consideration and inclusion in their spectacular event. We hope to present again at the next event with Two-Bit Circus.

Two-Bit Circus STEAM Carnival was a success! RRS glad to be there.

If anyone is interested in learning more about the RRS or having one of our rocket build events at their school or at a private event, please contact Larry, our events coordinator.

events@rrs.org

The RRS also works with several universities providing both technical assistance and a private site for testing in the Mojave Desert. For interest in using the RRS testing site, contact the RRS president, Osvaldo Tarditti.

president@rrs.org

Or you can just stop into one of our monthly meetings at the Ken Nakaoka Community Center in Gardena on the 2nd Friday of each month at 7:30pm. Next meeting will be June 8, 2018.