# Tesla valve : how does it work?

## The valve : An overview

All valves shown in fig 1, have one thing in common: they all have moving parts. In this article, I will explain how Nikola Tesla achieved a one way valve without any moving parts. Let's get into it.

## Invention of Tesla valve

Is it possible to design a one-way valve without any moving parts? Most of us will feel like this is an impossible design challenge, but not for design genius Nikola Tesla. Nikola Tesla had developed a one-way valve without any moving parts (refer fig 2). In his patent, he named this valve a ‘valvular conduit’. In this article, I will explain you the working of this valve with different designs.

## First design : undulations on wall

Let’s consider the simple design shown in fig 3. a simple channel with some undulations on the walls. These types of undulations provide the same amount of resistance to flow when fluid enters from any side.

## Second design : converging and diverging flow

Now, take the second case(refer fig 4a). Here, the obstacles are added at an angle as shown. The interesting question for you: in which direction will the fluid find it easier to flow—left to right, or right to left? Your intuition says that the right-to-left flow is easier, doesn’t it? Why is this so?

The flow is the converging type when it goes from right to left, but the diverging effect will take place when the direction of the flow is reversed. The physics of converging and diverging flow are quite different. In converging flows, as the area reduces, the velocity will increase along the flow. This velocity increase means that the pressure will drop along the flow(refer fig 4b).

For diverging flow, the case will be exactly the opposite; the pressure will increase along the flow. This pressure increase is called an ‘adverse pressure gradient’ condition. As the pressure increases along the flow, the fluid particle decelerates along the length, and after a particular length, flow reversal could occur(refer fig 4c). This reversal will lead to flow vortices and energy losses. In short, diverging flow is a difficult flow to maintain; it offers far more resistance than a converging flow.

## Third design : obstacles connected to the wall

Let’s rearrange the obstacles of fig 4a. Here, few obstacles are connected to the wall and the ones remaining are made smaller (refer fig 5a). Let’s examine what happens to the flow when it moves from left to right. As you can see, the flow is getting divided into two parts along with the flow divergence. After this the secondary streams are directed to mix with the primary stream almost in 180 degrees angle. This process is similar to mixing two jets from the opposite directions, which results in whirling of the flow and losses. This design will obviously produce more restriction than the previous design, and this process will repeat at every pair of obstacles. When the flow goes from right to left (refer fig 5b), it passes very easily, without much obstruction.

## Tesla’s design structure

Let’s make a few more geometrical modifications to this design. The previous design (refer fig 5b) is a mirror reflection. Let’s shift the lower portion, as shown in fig 6a. Now the width of the obstruction is increased. What you’ve got now is Nikola Tesla’s design. In the Tesla valve, the flow is always divided into two streams. The straight line flow is the primary stream and the diverted flow is the secondary stream. In his design, Nikola Tesla cleverly integrated all the interesting fluid mechanics we have learned so far in an optimum way.

## Tesla Valve : detailed mechanics

Now let’s see the detailed fluid mechanics of the tesla valve. Let’s consider the right-to-left flow, first (refer fig 6b). Initially, the flow is divided into two streams. Obviously, the secondary flow will be very low since the fluid has to take an unnecessary turn to enter that region. This means the majority of the flow will be due to the primary stream, and it will go almost in a straight line, without much obstruction.

When fluid enters from the left (refer fig 6c), the flow again gets divided into two streams. In the bottom section the flow diverges, and the adverse pressure gradient will make life difficult for it. The second stream hits the bucket-like structure and loses its momentum. After this momentum loss, the flow takes an approximate 180-degree turn, which again causes flow losses. After all these hurdles, this stream mixes with the first stream, from an opposite direction, resulting in further energy loss. In short, when the flow goes from left to right, it undergoes a huge amount of obstruction.

This process of sudden expansion, deflection, reversal, and mixing will take place at every unit. By adding many such units, the resistance can be further increased.

I hope you have learned how Nikola Tesla designed a one way valve without any moving parts.