Jiggle Valve design feature with the PRT

As we all know the later design of the thermostat is the "PRT".
Prior to this the thermostat was located at the cylinder head. With the early system it included two "jiggle valves" (one at the cylinder head and one in the up-&-over hose close to the other end of the cylinder head where one hose join the water rail).

The PRT system retained the jiggle valve in the cylinder head, and we can debate the usefulness of that, but the other appears to be omitted. As the jiggle valve is intended to dispel air but seal against water flow that means that there must be a continuous flow of water to the expansion tank with the PRT arrangement via the 4-way connector.
Is this correct? If not where is the other jiggle valve please? 
If no second jiggle valve should there be another restrictor in addition to the one that fits against the water rail to improve the flow to the heater? If so what size and where does it fit?

What car are you talking about? Because the F & TF never had thermostats housed in the heads, but on the side of the motor under the intake manifold.

It is the TF135 that I wish to convert to the PRT system from the style where the old stat is on the end of the water rail and slips into the engine close to the bottom of the head on the off side.
So my question is basically why do I not need a second jiggle valve?
Did the later TF135's fitted with a PRT have a 2nd jiggle valve? If not why not as they must have experienced water squirting into/across the expansion tank. 

I’m unsure what difference, if any between the tf135 & my fVVC, when fitting a PRT.
It was some good while ago, & the memory fades, however I simply bought the collection of pipe work, along with the PRT & neutered the original stat’.
All was well for a time until I realised the PRT wasn’t closing/opening properly; a new one was fitted & after I’d dried out normally service was resumed.
No jiggery pokery with the jiggle valve, nothing was discussed on the subject at the time & so nothing done.
Have I goofed?
M

I always thought the jiggle valve was to allow a small flow of water to pass a fully closed thermostat..so the pump didn't pump against a brick wall.

 

I think the purpose of the particular jiggle valve nearest the water pump (not the one in the thermostat itself) is to vent air. Some will argue that the ball should be removed to stop it blocking up.
In the earlier system (pre PRT) I suspect the other jiggle valve in the “up and over” hose is to stop it being air locked.
But it would vent any air too but with the ball sealing the vent it would prevent circulation.

So, if it is not fitted in the 4-way system there must be an unrestricted flow to the expansion tank. Exactly how vigorous will no doubt depend on the fluid dynamics. 
What I am seeking is someone with a PRT fitted as standard and to find if there is a jiggle valve in that small bore spur from the 4-way T to the expansion tank, and if there isn’t is there a continuous flow when the system has reached full operating temperature.
Anyone help please?

I get what you are saying and see the reasoning behind it. I hope someone can help you with an answer.
The jiggle valves in the thermostats I am used to have no ball to seal just a simple twisted piece of rod in the shape of a primitive mushroom!
Good luck!

The purpose of jiigle valves in cooling systems is to allow the cooling system to bleed any trapped air when the thermostat is closed.
Imagine if you had a large bubble of air trapped under a closed thermostat, the wax pellet that opens the thermostat might not be imearsed in the water and then wouldn't know that the water was too hot and not open!

Happy New Year to one and all!

Cobber, thanks for engaging in this. I get what it’s for when it is a small hole in the thermostat.
The floating valve giggle system located at the engine close to the thermostat is intended to pass any entrained air to the expansion tank. The ball then floats in the coolant before sealing with minimal flow (if any) passing through it.
In the pre PRT cars there is another in the “up and over” hose at the other end of the engine. In the PRT cars there is no “up and over” hose it is not required and uses a 4-way “T” piece.  In that case water has an unlimited flow path to the expansion tank unless something else is included instead. 
If there is something to include what is it please?
Is that restriction needed or is free flow vital .
It would be very helpful if someone with a factory fitted PRT could report if there is a small steady flow across the tank from that small hose to the expansion tank once up to temperature from the 4-way T.

I would imagine that any aditional jiggle valve would serve the same purpose of evacuating air that has a habit of collecting at that point, without  allowing a full flow which would  pehaps divert flow from where it's needed, or even over cool an area.

I stand corrected on the purpose of the jiggle valve..but M'Lord..in all my years of fixing cars I have never discussed such a valve.

I hope you can find a conclusive answer as to the need of one.

I have a 2004 TF 135.  It has a PRT and I have always assumed that it is standard for the car. 

I have to confess to knowing almost nothing about the jiggle valves.  I assumed my car must have one (or more) but I have no idea where it is or what it looks like! I remember from the thermostat in my Austin A35 that it had a strange little dangly metal bit hanging through a small hole in the metal ring around the stat.  I never knew what it was; was that a jiggle valve?

What I can say, with some degree of certainty, is that water pumps into the expansion vessel right from starting the engine.  It can be seen quite clearly with the pressure cap removed.  I have assumed that this is normal.

Does this help at all?  It's chucking it down now, but I am happy to check it out if it answers any questions.