immersion heater

What is an immersion heater?

August 22, 2022 by Jamie Bristoll

[youtube https://www.youtube.com/watch?v=oroE6nVFzo0&w=560&h=315]

An immersion heater is, simply put, a number of elements, usually 3, elements, a screwplug and a IP rated terminal box to protect the connections.

screwplug sizes — …one of these, drilled through, for the elements to be braised or welded into…

Terminal box — …and one of these to attatch to the screwplug, to house the terminals and wiring.

And, in the best Blue Peter traditions, here’s
one we made earlier…

The heater is then screwed throught the side of the tank using a weld boss…

Mild steel tanks require mild steel weld bosses, and likewise, stainless steel tanks require horribly priced stainless steel weld bosses. I’ll tell you what brass bosses are used for when I find out.

Immersion heater screwplug sizes

July 24, 2022 by Jamie Bristoll

Examples of some of the various screwplug sizes available, these are undrilled, therefore can be used as a blanking plate or for our customers who are unsure of their requirements, to screw into their socket before anything is manufactured bespoke. Very useful!

This is the simple version,

BSP “	DIAMETER ACROSS THREAD “
1/2	.825
5/8	.902
3/4	1.041
7/8	1.189
1	1.309
1 & 1/4	1.650
1 & 1/2	1.882
1 & 3/4	2.116
2	2.347
2 &1/4	2.537
2 & 1/2	2.95

…and this is the complicated version,

	Thread Form Type	Major Diameter mm d=D	Pitch mm p	Threads per inch tpi	Pitch Diameter mm d2=D2	Minor Diameter Male Thd. d3	Thread Height H1	Tap Drill Diameter mm
1/8 “	BSPP/BSPF	9.728	0.907	28	9.147	8.566	0.581	8.7
1/4 “	BSPP/BSPF	13.157	1.337	19	12.301	11.445	0.856	11.6
3/8 “	BSPP/BSPF	16.662	1.337	19	15.806	14.95	0.856	15
1/2 “	BSPP/BSPF	20.955	1.814	14	19.793	18.631	1.162	19
5/8 “	BSPP/BSPF	22.911	1.814	14	21.749	20.587	1.162	20.75
3/4 “	BSPP/BSPF	26.441	1.814	14	25.279	24.117	1.162	24.5
7/8 “	BSPP/BSPF	30.201	1.814	14	29.039	27.877	1.162	28
1 “	BSPP/BSPF	33.249	2.309	11	31.77	30.291	1.479	30.5
1 1/8 “	BSPP/BSPF	37.897	2.309	11	36.418	34.939	1.479	35
1 1/4 “	BSPP/BSPF	41.91	2.309	11	40.431	38.952	1.479	39.5
1 3/8 “	BSPP/BSPF	44.323	2.309	11	42.844	41.365	1.479	41.5
1 1/2 “	BSPP/BSPF	47.803	2.309	11	46.324	44.845	1.479	45
1 3/4 “	BSPP/BSPF	53.746	2.309	11	52.267	50.788	1.479	51
2 “	BSPP/BSPF	59.614	2.309	11	58.135	56.656	1.479	57
2 1/4 “	BSPP/BSPF	65.71	2.309	11	64.231	62.752	1.479	63
2 1/2 “	BSPP/BSPF	75.184	2.309	11	73.705	72.226	1.479	72.5
2 3/4 “	BSPP/BSPF	81.534	2.309	11	80.055	78.576	1.479	79
3 “	BSPP/BSPF	87.884	2.309	11	86.405	84.926	1.479	85.5
3 1/4 “	BSPP/BSPF	93.98	2.309	11	92.501	91.022	1.479	91
3 1/2 “	BSPP/BSPF	100.33	2.309	11	98.351	97.372	1.479	97.75
3 3/4 “	BSPP/BSPF	106.68	2.309	11	105.201	103.722	1.479	104
4 “	BSPP/BSPF	113.03	2.309	11	111.55	110.072	1.479	110.5
4 1/2 “	BSPP/BSPF	125.73	2.309	11	124.251	122.772	1.479	123
5 “	BSPP/BSPF	138.43	2.309	11	136.951	135.472	1.479	136
5 1/2 “	BSPP/BSPF	151.13	2.309	11	149.651	148.172	1.479	148.5
6 “	BSPP/BSPF	163.83	2.309	11	162.351	160.872	1.479	161.5

I hope these are useful for reference purposes.

More importantly for us, on a daily basis, are the following limitations as to what will fit onto the smaller screwplug sizes. We deal with up to 2.25″ only, with 2.5″ being accommodated by fitting a brass adaptor to 2.25″ screwplug.

2.25″	TROMBONE 2 STAT
2″	TROMBONE 1 STAT
1.75″	TROMBONE 1 STAT
1.5″	3 HAIRPINS 1 STAT
1.25″	3 HAIRPINS NO STAT

Anything smaller than a 1.25″ screwplug will be limited to 1 element, having immediate implications for the achievable watts density. Likewise, being limited to U bends only, makes reducing the watts density more problematic. Many domestic and commercial plumbing applications use 1.5″BSP, and are thus limited to 3 hairpins and only 1 stat pocket. maximising the immersed length of those U’s is all that can be done to reduce the watts density. To overcome the issue of only 1 stat pocket, we find ourselves increasingly selling dual control and cutout stats.

By hairpin, we mean a U bent element, and trombone indicates double looped. To determine what element is suitable, for U’s you merely double the maximum immersed length available, ie, 24″ immersed length will use u bent 48″ elements. However, if double looping is possible due to the screwplug size and other factors relating to the application (cleaning, etc), that 24″ maximum immersed length could be multiplied by up to 3.5, allowing the use of 84″ elements. See the watts density article to appreciate what a difference that will make. 48″ to 84″ almost double the hot element available, so is almost going to halve the watts density. A big issue on little screwplugs.

Ingress Protecion ratings for immersion heater terminal box

July 24, 2022 by Jamie Bristoll

What is Ingress Protection?

IP Explanation and Ratings
EN 60529 outlines an international classification system for the sealing effectiveness of enclosures of electrical equipment against the intrusion into the equipment of foreign bodies (i.e. tools, dust, fingers) and moisture. This classification system utilizes the letters “IP” (“Ingress Protection”) followed by two or three digits. (A third digit is sometimes used. An “x” is used for one of the digits if there is only one class of protection; i.e. IPX4 which addresses moisture resistance only.)
Degrees of Protection – First Digit
The first digit of the IP code indicates the degree that persons are protected against contact with moving parts (other than smooth rotating shafts, etc.) and the degree that equipment is protected against solid foreign bodies intruding into an enclosure.

0 – No special protection.
1 – Protection from a large part of the body such as a hand (but no protection from deliberate access); from solid objects greater than 50mm in diameter.
2 – Protection against fingers or other object not greater than 80mm in length and 12mm in diameter.
3 – Protection from entry by tools, wires, etc., with a diameter of thickness greater than 1.0mm.
4 – Protection from entry by solid objects with a diameter or thickness greater than 1.0mm
5 – Protection from the amount of dust that would interfere with the operation of the equipment.
6 – Dust tight.

Degrees of Protection – Second Digit
The second digit indicates the degree of protection of the equipment inside the enclosure against the harmful entry of various forms of moisture (e.g. dripping, spraying, submersion, etc.)

0 – No special protection.
1 – Protection from dripping water.
2 – Protection from vertically dripping water.
3 – Protection from sprayed water.
4 – Protection from splashed water.
5 – Protection from water projected from a nozzle.
6 – Protection against heavy seas, or powerful jets of water.
7 – Protection against immersion.
8 – Protection against complete, continuous submersion in water.

How to choose a water immersion heater

July 23, 2022 by Jamie Bristoll

Remembering all of the aspects and considerations discussed on the “How to choose an immersion heater” page, water hardness must be taken into account when designing a water immersion heater.

A detailed description of water hardness can be found HERE, but for the purposes of this blog, we will say that hard water has a higher concentration of calcium and magnesium which leads to limescale, which we are all familiar with in kettles, etc, within the home. Whilst merely being an inconvenience in the home, (if I can’t taste it in my tea, and remember not to look in the kettle when filling it, I can pretend it’s not there) it can be a real issue in commercial and industrial applications.

The problems are caused by the limescale deposits building up on the hot part of the elements. Once this process starts, it becomes self perpetuating, and indeed self accelerating, if not removed by jet washing or other means. Basically, the limescale build up prevents the heat getting away from the element, acting like an unwanted insulating jacket, increasing the element surface temperature, which in turn, attracts more deposits. An example of which is shown below, courtesy of gimmecoffee.com, which would perhaps be better used as a christmas tree than for making coffee!

The easy way to maximise the working life of your immersion heaters, whether in a hard water area or not, is to minimize the Watts density. The article explains in detail a simple concept which we are using every day, maximise the element length THUS minimising the watts density THUS maximising the working life of the element, all other things being equal.

How to choose an oil immersion heater

August 17, 2021 by Jamie Bristoll

In addition to all the requirements for water immersion heaters, for oil heaters our target is to get the watts density down, requiring more element or less power, that is the compromise facing the customer, who is always right, even when they are wrong!

For HEAVY INDUSTRIAL OILS we are aiming for <=12w/in².

For LIGHT COOKING OILS we are good with up to 25w/in².

If we stray above this, the sheathe temperature is too high, the oil caremelizes onto the elements, thus preventing dissipation of the heat, so it gets hotter & more stuff sticks, until something goes BANG!

POIL Oil Imersion Heater — Oil Imersion Heater

The FOIL Range has many benefits, including bespoke screwplug size, immersed length, double stat pockets, etc, all with a 2 week leadtime. The 8mm elements can be double looped to fill your maximum available immersed length with a large overall length of element.

On 2″BSP & above screwplugs, the elements drop from the screwplug to your maximum available immersed length, before looping back up to within a few inches of the screwplug (taking care not to stray into the cold section), before dropping back to full immersed length, then returning back up to the screwplug. This allows us to fit nearly twice the length of element possible in a plain U bent element. For example, in 24″ of maximum immersed length, we could use an 84″ element double looped. Thus, nearly halving the resultant watt density.

If you are in the privilidged position of having a very large tank with a massive space available for immersed length, you may choose not to double loop, but to have plain U bent elements over a meter in length.

But for most folks, size is important! And this is where compromise is required to achieve the target watt densities shown above.

What is an immersion heater?

Immersion heater screwplug sizes

Ingress Protecion ratings for immersion heater terminal box

What is Ingress Protection?

How to choose a water immersion heater

How to choose an oil immersion heater

Advertise here!

Credits

Disclaimer