I got this from Atkinson's, they are having problems posting themselves:
Hi all, we spotted threads on this forum, tried to reply but the system took the long post as spam so thought I would register to answer any queries.
Top off take systems are a bit more complex than standard gravity feed and often certain service aspects are overlooked causing issues down the line....which are then often attributed to the valves themselves.
To my knowledge I don't believe we have actually had a faulty Tanktop valve in itself(10+ years!), the issues are the serviceable parts around them. As standard unless otherwise specified the Atkinson Tanktop units are supplied with 1.7m of suction pipe which we say accommodates for a main tank height of 1.5m - there should always be around 20cm excess of pipe which ensures a loop is created at the bottom and ensures the end of the pipe is submersed in fuel. We also set the anti siphon valve to 150mb as standard which equates to 1.6-1.7m of drop in the line being protected from siphoning. If the main fuel tank is deeper than this then a longer suction hose is required. If the total drop in the line is more than 1.7m then the unit should be calibrated by us upon ordering(the top module can also be sent back for calibration).
The fact they are pulling from the top of the tank and have an anti siphon valve is why usually they will be fitted with the need for a Tigerloop for burners or oil lifters for Aga(wick) type appliances. The resistance of the anti siphon valve is the equivalent of having a lift in the line rather than having a gravity feed, so the burner pumps need to be opened into a 2 pipe system which allows the pumps to have a greater suction. Tigerloops allow for a 2 pipe system to be created without returning to the tank + allow the air(from the oil being in a state of negative pressure) to aspirate from the return loop. Wick fed appliances need gravity feed so an oil lifter would be necessary.
One of the main service issues overlooked will be the floating suction pipe, this is made out of rubber and suspended in the tank so that it can draw oil from the top of the fluid. Being rubber and fitted outside suspended in kerosene this pipe will need to be checked and nipped up at the top connection to the Tanktop from time to time - we recommend annually upon boiler service along with checking of the filter in the Tanktop. A leaking joint will allow air to leak in without leaking oil out as the line will be under negative pressure. Also these are usually fitted around the same area as the fill point and inspection cap, its quite common for delivery drivers to just put their nozzle into the inspection cap and fill up at various angles which at up to 4-500lpm and 8 bar pressure will tie into the need to check and tighten the suction pipe. Since January 2020 the rubber pipe is a very premium automotive quality hose which I am unware of any hardening as yet. Older hoses will probably harden after a couple of years an need replacing, if they harden then you can either experience not being able to seal at the top connection or in extreme cases the rubber hose staying up as a hard loop and the oil level dropping below it.
On the outlet usually we supply the valves with a 10mm push fit. Some tank manufacturer specific kits come with a flexi pipe and another push fit for hard pipe connection outside of the tank. When using a push fit with flexi pipe it is important to have ample slack at the push fit connections as the elasticity of the pipe against the internal sealing o'ring on the push fit will cause it to give way if it is taught. If using a hard pipe connection directly into the push fit it is important to have it very straight and free from burrs, pull back the collar insert pipe then release - simply pushing in hard pipe at potential angles could catch the o'ring and cause damage. The option is there to remove the push fit and install a 1/4" - 10mm stud for hard pipe connection.
Finally in the case of tanks with support struts moving across the mid section or maybe very thin shapes - the suction pipe has the potential to get caught. We manufacture a version suitable for rigid suction pipe connection which is supplied with a 10mm compression fitting for the suction pipe. The engineer can then use 10mm copper pipe to make their own suction to the bottom of the tank - recommend bending a hook at the bottom to avoid pulling from the very base of the tank where sediment and water will gather. Obviously in this case it draws from the bottom of the tank but the point it draws from can be tailored somewhat, the main benefit of the Atkinson Tanktop at this point would be the anti siphon valve over a gravity feed tank.
If any further advice is needed or general questions let me know,
Matt - Senior Technical Manager
Atkinson Equipment Ltd
Best regards
Matt Lurc
Senior Technical Sales Manager
Atkinson Equipment Limited
Tel: (01373) 822220 ext. 239
DDI: (01373) 821617
Fax: (01373) 826996
