Exploration With Different Valve Connections

An important part of a pneumatic system are valves. These were examined to test which is the most air-tight. Depending on the manner of connection (tapping or screwing) a softer or harder material should be chosen. Further, printing circular forms perpendicular to the printing direction, will cause oval-like shapes in soft and flexible materials due to the weight on top of the print. This phenomenon could be observed in a prototype of a John-Guest connection.

Below you can see the cross-sections of the different connections, from top to bottom post threaded connection (used in the one-way valves and gripper), pre threaded connection and a John Guest connection.

Post-Tapped Thread Connection

Pre-Tapped Thread Connection

John Guest Connection


Printing One-Way Valves

We explored if it is possible to print one-way valves. Two prototypes were printed and both works surprisingly well. Although some air is still leaking out (because of the cleaning process to remove support material as it damaged the enclosed parts), it demonstrates that functional parts can be printed quite easily.

Below you can see the cross-section of both valve designs. The blue parts are the enclosed and can move around. The reds parts are seals made from softer material so the moving part can fully close one direction if pressure is applied from one side.

Ball One-Way Val

One-way valve based on a free-moving ball in an enclosed space. The ball is not able to close the upper output due to the form of the enclosed space, however it is possible for the ball to close the bottom output because of the sealer.


Plug One-Way Valve

One-way valve based on a plug-like object. The plug can make an up an down movement to change the state of the valve. The top part is completely solid (and can therefore close the valve), while the bottom one has air inlets.



Blowing up Fingers!

To get an idea of how our models will behave once printed, a Finite Element Model Analysis (FEA) was conducted with the gripper-finger models. This analysis is a non-linear regression model, which can simulate quite accurately large and complex deformations in materials, under complex load applications and boundary conditions. As we do not know the right material properties just yet, we have applied representative figures for the properties. This is to get an idea on how the bellow shapes will behave in reality (i.e. to know if we can expect a bending motion or a stretching etc.)

Right now, one simulation was done to test how well the simulations work. This simulation can be watched below. It should be noticed that the program does not take self inflicted collisions into account yet. This means that the solid can intersect itself when blown up, which would in reality induce more deformations in bending direction for this model.

Screenshot of a FEA in CATIA

Screenshot of a FEA in CATIA

Animated GIF of FEA

Animated FEA in CATIA

Testing Material Properties

Today we conducted a tensile strength test on the three specimens which we made previously (1). We started our testing at the faculty of Industrial Design Engineering (IDE) with a universal testing machine (UTM) which was made by a student. However due to problems with the software, we could not get results with it. We therefore went to the 3me faculty to do the test with a ZwickZ100 UTM (2) in combination with an extensometer (which was used to more accurately measure the change in length of the specimen).

From this test we learned that the ridged specimen breaks at 40.64 MPa and the composite at 10.27 MPa (however the last one broke not in the middle, but the bottom part was ripped off). The UTM machine was not able to measure the most flexible material as no force was build up for measurement.

Next week, we will do more tensile testing, again with the soft material, but also with another new specimen (60% ridged, 40% soft material) as this will probably be the composite material we will use for the gripper-finger.


First tensile strength test set-up at IO. However because of software problems this did not work well.


The ZwickZ100 UTM just broke the rigid specimen in half.


Remains of the specimen.

(1) Weblog post, 1 October 2015, https://softrobotics2015.weblog.tudelft.nl/2015/10/01/connex-printing-test/
(2) Zwick Roell Group, http://www.zwick.com/