Water tank connection?

[Stehughesie]

Hi.

Hoping for some advice as struggling....

I want to connect new water pump to water tank. The tank has a 3/4" male thread and the new pump has 1/2" male plastic thread. I've thought of using a flexi hose but concerned the rubber washer will get damaged against the brass 3/4" tank. Been to plumbers a load of times, tried different fittings, lost sleep, any advice gratefully received. Picture shows old pump (although new pump is identical) and male 3/4" Gatwick valve that new pump will attach to.

Thanks 

Ste

[cheesegas]

Is it a Shurflo pump? Use the 1/2" female to hose tails which it comes with - the thread isn't a 1/2" BSP or BSPT thread, it's 1/2" NPT which means nothing down the plumber's merchant will fit. BSP will kind of go on but may leak.

 

Once you've fitted the 1/2" NPT to 1/2" hose tail to the pump, you can then fit a 1/2" hose tail to 3/4" BSP female adaptor to the water tank outlet. Join the two with a short length of 12mm food safe hose and stainless jubilee clips. This has the side effect of isolating the pump's vibrations and making it quieter too.

 

I'd recommend changing the gate valve for a quarter turn ball valve though, the gate valves have a habit of seizing or leaking when shut.

[Stehughesie]

Thanks mate, appreciate the help. 

Yeah, pump is shureflow and it has 2 parts that screw on to either side of the pump. I assume they are the 1/2" NPT? These have flanges on for a hose pipe to slide on.

So attach these parts, get 12mm food safe hose and jubilee clip on. Bit I'm stuck on is the 1/2 hose rail to 3/4 bsp female adaptor at tank? Not sure what these are...

Sorry to be a nuisance 

[Tony Brooks]

Hose TAIL, or hose barb

 

[Stehughesie]

Thanks mate, appreciate the help. 

Yeah, pump is shureflow and it has 2 parts that screw on to either side of the pump. I assume they are the 1/2" NPT? These have flanges on for a hose pipe to slide on.

So attach these parts, get 12mm food safe hose and jubilee clip on. Bit I'm stuck on is the 1/2 hose rail to 3/4 bsp female adaptor at tank? Not sure what these are...

Sorry to be a nuisance 

[cheesegas]

9 minutes ago, Stehughesie said:

Thanks mate, appreciate the help. 

Yeah, pump is shureflow and it has 2 parts that screw on to either side of the pump. I assume they are the 1/2" NPT? These have flanges on for a hose pipe to slide on.

So attach these parts, get 12mm food safe hose and jubilee clip on. Bit I'm stuck on is the 1/2 hose rail to 3/4 bsp female adaptor at tank? Not sure what these are...

Sorry to be a nuisance 

Perfect, don't attach anything directly to the pump except those Shurflo 1/2" to NPT hose tails.

The thread on the valve will most likely be BSP tapered, so you'll need something like this to go from 3/4" BSP-T female to 12mm male hose barb.

https://www.ebay.co.uk/itm/225312832551

 

BSP taper threads seal on the thread itself rather than a washer, so you'll need to wrap a couple turns of PTFE tape on the threads.

Edited April 15 by cheesegas

[jonathanA]

Whilst cheesegas is correct these pumps do have npt threads, In my experience bsp fittings are a good fit and don't leak. Although some care is needed and you need to check the mating faces are compatible.  I use flexible connector hoses and speedfit connectors all readily available from screwfix. 

 

It's hard to tell what the gate valve is fitted to but it's worth trying to do away with it. If all else fails I'd leave  the gate valve and fit something better after it (but close) and just ignore the gate valve. 

[cheesegas]

19 minutes ago, jonathanA said:

Whilst cheesegas is correct these pumps do have npt threads, In my experience bsp fittings are a good fit and don't leak. Although some care is needed and you need to check the mating faces are compatible.  I use flexible connector hoses and speedfit connectors all readily available from screwfix. 

 

It's hard to tell what the gate valve is fitted to but it's worth trying to do away with it. If all else fails I'd leave  the gate valve and fit something better after it (but close) and just ignore the gate valve. 

The Shureflo pump is a weird one - the fittings don't seal on the thread and they don't seal on a mating face either, which is why I'd recommend using only the Shureflo fittings. Hard to describe but there's two concentric raised rings on the fitting, and the male bit on the pump fits snugly between the rings to form the seal. My boat had someone put a BSP tap tail on the pump with a lot of PTFE tape which leaked constantly until I swapped it out for the Shureflo part.

[Ronaldo47]

The 1/2" and 3/4" pipe threads are the only ones where BSP and NPT have identical pitches (14tpi).  

 

My screw thread book gives the BSP/NPT pipe diameters for 1/2" as 0.8250"/ 0.840" and for 3/4"  as 1.0410"/ 1.050". 

 

BSP/ NPT thread flank angles are 55°/ 60°. BSP threads have rounded crests and roots, those of  NPT are flat.   If the fit is tight, using a die/tap on/in the  larger/smaller thread should provide a solution.

[cheesegas]

7 hours ago, Ronaldo47 said:

The 1/2" and 3/4" pipe threads are the only ones where BSP and NPT have identical pitches (14tpi).  

 

My screw thread book gives the BSP/NPT pipe diameters for 1/2" as 0.8250"/ 0.840" and for 3/4"  as 1.0410"/ 1.050". 

 

BSP/ NPT thread flank angles are 55°/ 60°. BSP threads have rounded crests and roots, those of  NPT are flat.   If the fit is tight, using a die/tap on/in the  larger/smaller thread should provide a solution.

I agree that the threads are similar enough to fit, but as mentioned above, the way it seals is different to both a tapered and parallel threaded pipe connection. I've got a spare Shurflo hose tail somewhere, I'll dig it out and get a photo - the tail fits into the pump without sealing on the threads or a face, it kind of clicks in between plastic flanges.

[Stehughesie]

Thanks everyone. Amazing advice.

I'm going with the shureflo tails out of the pump, 12mm food safe hose, 3/4 to 1/2 inch hose tail screwed onto male water tank thread with ptfe and tightened up with jubilee clips.

At other end I'm going with shureflo tail, 12mm food safe hose then JG soeedfit 1/2 to 15mm connector. This leads to accumulator and then into main boat.

Thank you everyone who has helped, much appreciated