Danfoss Pressure Switch

Hello,

I'm having difficulty trying to attach a Danfoss pressure switch. It is attached to a compressor I bought for my project restoration. It was badly attached to the tank via a flexible hose with clamps at the end. This is not the original attachment. I thought it was an easy fix with a coupler until I found out that all my swivel coupler won't fit. I was a bit puzzled by the pressure switch attachment. I measured the outside thread with a micrometer and it reads .430 of an inch. Is this a standard size thread/attachment? Hope somebody here will shed some light on this. Thanks in advance.

Raphael

Is it a tapered thread and if it is it may be 1/4 x 19 TPI BSPT. ( British Standard Pipe Taper Thread) Measure for a taper and a picture may help.

David

Another possible option is 1/4 NPT thread. This is .54in O/D * 18 TPI.

Cheers

John

It will almost for sure be BSP so 1/4" is favorite. I will try and check one later today for you. It is most unlikely to be NPT, or any metric. The Danfoss switch has a female thread ? Noel.

Too small for 1/4 BSP.

Non BSP pipe / fluid / air connection threads are a major nightmare for " ..... can fixit" folk. All sorts of weird and wonderful stuff out there.

At 0.430 measured outside diameter I'd plump for 7/16 UNF, which is 20 TPI and not uncommon for such duties.

Another possibility is 12 mm x 1, 12 mm x 1.25 or 12 mm x 1.5. Over the years I've needed taps for all three!

As a side note 7/16 UNF is often found in the cast alloy handles of Far East import air tools with a male BSP parallel adapter screwed in. A right pain when someone wants you to fit a QD air connector directly to the handle after wrecking the original getting it out. Super Godzilla level threadlocker-sealant being the norm.

Clive

Quick rummage in the workshop turned up this Danfoss pressure switch which has a 7/16 x 20 UNF male connector

That is an industrial one made in Denmark. Lower end  Danfoss branded ones made in Poland or Far East tend to be BSP.

SIP and many of the other hobby compressors often use M12 x 1 for the regulator connections even when the switch is BSP.

Clive

Edited By Clive Foster on 16/04/2021 10:29:12

Just a Friday morning thought.

Might it be a flare nut fitting at 1/4” SAE?  Male = .44” OD if my memory serves well.

It’s about 20 years since I dealt with those fittings so ignore if I’m talking rubbish.

Edited By V8Eng on 16/04/2021 11:32:07

Thanks for the input gents. Here is the said thread. I looked at the NPT chart and the 1/4 had 18TPI, 7/16 drill size and a decimal equivalent to 0.4375. Its closer to the OD mic measures I made at .430 but im still confused Noel mentioned that it is unlikely NPT. Also Clive mentioned UNF 7/16. Im sure 1/4 BSP is to big as I tested it already. So is this 1/4 NPT or UNF?

Looks the same as Clive posted.

That one is 7/16 - 20 UNF thread for a flared fitting. Most likely SAE 45°. Parallel thread adapater with tape was used on whatever I salvaged mine from.

But need to be careful with SAE threaded flare fittings.

Brake pipes can use 7/16 - 24 tpi. JIC and SAE flare fittings are 7/16 - 20.

See

**LINK** , https://brennaninc.com/wp-content/uploads/2011/09/BrennanThreadChart.pdf

and

**LINK** , https://toplinemachinery.com/pages/jic-fittings-size-chart

Not forgetting that JIC uses a 37° flare whilst SAE is (supposed to be) 45°.

I've been known to be somewhat eloquent when running down those particualr rabbit holes whilst unbodging things!

Clive

Edited By Clive Foster on 16/04/2021 11:49:21

Edited By Clive Foster on 16/04/2021 11:49:43

Clive, the one I have looks very similar to your Danfoss connector. Is it likely 1/4 UNF?

It looks like a flare fitting as used in refrigeration systems, so probably SAE 1/4".

Peter

Raphael

Found the specification for my Danfoss switch on line which says the connection is 1/4" DIN 8906.

**LINK** , https://store.danfoss.com/en/Climate-Solutions-for-cooling/Switches/Pressure-Switches/Pressure-switch%2C-KP5/p/060-117166 . Maybe yours is somewhere on same site.

A bit more searching confirmed that DIN 8906 is 7/16" - 20 with a 45° degree angle. Common on refrigeration fittings although they seem to specify the full 90° cone angle rather than the half angle 45° flare.

See table 3 here.

**LINK** , https://www.jiayuanfitting.com/info/din-8906-refrigeration-flare-type-fittings-44302832.html

Hopefully thats sorted it.

Clive

Edited By Clive Foster on 16/04/2021 12:06:26

Thanks Clive. I was looking at the chart. So its UNF 1/4 with 20 TPI? I plan to just get an adaptor so the end angle will not be needed. I plan to get an adaptor for the 1/4 UNF to 1/4 BSP then the rest is straightforward, hope this is ok i guess?

Raphael

I can see on the chart (Table 3) that the 1/4 UNF is tabulated with 1/4 NPT? but the thread TPI is different? Sorry for the questions as im trying hard to understand it. It seems like it is an adaptor male to male NPT to UNF?

Raphael

Edited By Raphael Golez on 16/04/2021 12:19:15

Raphael

The adapter sounds like a plan.

Mine has such an adapter fitted. Simple parallel threads with plumbers tape to seal. All seems to have worked satisfactorily as everything was "well used" grubby.

1/4" is the pipe size.

Different threaded fittings can be used on the same size pipe but you have to match thread types so BSP screws onto BSP, NPT onto NPT, UNF onto UNF et al. Its all a bit confusing until you realise that.

Clive

Edited By Clive Foster on 16/04/2021 12:24:55

Cheers Clive! I have ordered my adaptors now. Hope it will be ok. I will update you with the results and hopefully its all good.

The threads on those Pressure Switches i would expect to be 7/16" SAE which was a standard thread for refrigeration 1/4" copper flare

David

Hi Clive, got the pressure switch connected. It is indeed 1/4 UNF - 20. Fully tested all pressure and air is holding without any leaks on the UNF-BSP adaptor. Really works a treat this small JUN Air silent compressor. I have done a full oil change with the specific compressor oil, cleaned all rubber seal and checked, changed air filter, checked all electrical and capacitor. Solid small silent compressor and the best thing is I bought the compressor in Ebay for .99 p as the owner said its for spare and its easier for him to just buy a new one than to try to fix it himself. Thanks for the help Clive!

Regards,

Raphael

Raphael

Great to hear that its all sorted.

The little Jun-Air is a nice quiet compressor. Used to have one in the optics lab to float the air isolated optical tables back when I was gainfully (?) employed.

Clive