Flow sensor for processor

[julesandtash]

Hi all,
I am just starting on my new control panel (after all I only got the relays and din PSU from b-r-t-p two years ago and the enclosure from Mark at the last BBB) and wanting to add some features.

One thing I really want is a sensor to prove that oil is flowing in the circulation loop. Whilst it is easy interlocking the heater to the pump power supply, that does not prove that the pump is pumping.
What I want is to generate a signal when there is flow in the pipwork.

I thought about pressure sensors but they could be fooled since the pump pushing against a closed valve would still generate pressure but no flow.

I have considered proper flow switches but they are lots of money.

Does anybody have a relatively cheap approach for proving flow. I dont need to measure flow rate, just show that there is a flow.

[Rotary-Motion]

quite a selection here jules

https://www.google.co.uk/#q=flow+sensor&hl=en&sa=X&tbo=u&source=univ&tbm=shop&ei=0H4BUdmlDYKyhAfkkYAg&ved=0CHUQzAMwBg&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&bvm=bv.41524429,bs.1,d.d2k&fp=2be2f32138bf0883&biw=1093&bih=447

[K.H]

Not sure if its the same thing but i have a pressure gauge inline and there is a big difference if something blocks or a valve is shut

[Rotary-Motion]

Not sure if its the same thing but i have a pressure gauge inline and there is a big difference if something blocks or a valve is shut

was gonna say stick a gauge in the pipe to see its working , but he may need an electrcal output for switching? maybe... ?

[Julian]

A taping either side of an orifice plate, connected to a differential pressure switch.  You might even be able to use the venture as the orifice ... can't remember if you use one on your new plant.

Or metal flap with magnet inside a plastic pipe, with reed switch on outside of pipe.

[Carrington]

I have some flow switches on some pumps I picked of from next door.
I think there inch wired into a LCD if they work your more than welcome to one when you pop up.
I will try and give them a test before your up

[photoman290]

i have a flap type with a reed switch you are welcome to if you want it i will venture in the yurt  of dreams,wet ones at the moment, and have a look

[julesandtash]

Excellent idea about the orifice plate b-r-t-p. I do have a venturi so maybe measuring the pressure each side of it would work.

Bob and Paul. many thanks for your offers, I would really appreciate having the units off of you so I have some options. That is most kind.

All of my pipe work is 1" BSP so Pauls sound ideal, not sure what size yours would be Bob (if you excuse the phrase!)

I already have a nice ajustable (1 to 12 seconds) time delay relay.
The idea will be that once the pump start button is pressed and released, the pump contactor will hold in for the period of the time delay (providing that the excess pressure sensor does not indicate a closed valve or blockage). If by the end of that period, the flow sensor has not indicated pump flow, the contactor will drop out and will stay so until the button is pushed again.

Keeping the start button pushed manually will over ride this feature allowing for manual clearing of a blocked pump or similar.
A second set of contacts on the relay controlled by the flow switch will also be the interlock to enable the heater to be energised only when flow is detected.

[photoman290]

not sure what size mine is havent looked for awhile . to stop it interfering  with the flow you could put it outside the flow with a one inch tee and a nipple and stop end, maybe with a valve so you can isolate it from the system. it will still detect a blockage but be out of the main flow. it has a flap so will interfere with the flow whatever size it is. should be less sensitive than a pressure detecting valve.